That’s actually far from accurate. This one particular boss is more of a puzzle that you need to solve, i.e. build a very specific party that, if played properly, can handle him quite consistently (I’ve been able to do it even with a blue portal without any useful treasures at all; besides, recently the player in PvE has been buffed to always win speed ties, making this potentially even easier), while a ‘generic’ party might indeed be overwhelmed quickly, and it’s quite a good puzzle at that, if you ask me. Of course, if your collection is limited and you lack some key mercenaries, then… tough luck, but otherwise it may be the… capacity of the players who complain that is ‘undertuned’.
The party I’ve done the bounty with multiple times is the following: Mutanus with the Irridescent Necklace (very important), Antonidas with the Cindercore staff (more of a support, probably could be replaced with Chi-Ji, but I haven’t tested it), Baron Geddon with the Mark of Conflagration (another crucial merc), Balinda herself, preferably with the fire elemental (skills don’t actually matter that much, she’s there for the equipment plus some help), Diablo with the Black Soulstone (the equipment is mostly useful for the climb) and Sky Admiral Rogers (equipment and skill levels don’t matter much, just don’t use the Ship’s Bell, put some Halting Sash on — or even nothing at all — instead), who can possibly be replaced with Cairne, especially since he should now always win speed ties against the wolf with Endurance Aura if it comes to that, but I haven’t tested it yet. I should add that I’ve had the key mercs maxed (even though I’m a 100% F2P guy, but I suppose I’ve farmed too much…), but I’ve highlighted some of the most important skills for this one.
The idea, of course, is to exploit the bonus that the warlords give to both teams. While Frost damage is probably not the strongest, if you ask me, since your mercs lack good AoE abilities, the Fire team, on the other hand, has some excellent options. Geddon, of course, with his Inferno is worth two mercs, since, due to the huge damage bonus, the amount of fire waves is nearly decisive, and he’s also a Caster; someone has got to trigger the combo effect for him, and that’d be Antonidas (do NOT use Ragnaros, since Drek’Thar can oneshot him immediately, ruining your strategy, and Balinda might just get destroyed too quickly, but Antonidas will do); and finally, your finisher is Diablo with his signature Fire Stomp for some massive damage to clean up those numerous enemies, so that only the boss or nothing remains. Rogers is mostly there to speed him up, since one of the wolves has the Endurance Aura (the idea was to be always able to win the speed tie no matter what, therefore I picked her over Cairne back in the day; besides, she is blue, which is also advantegeous, but Cairne might also work).
For the climb, you will be mostly using Mutanus, Diablo and Geddon: the former one is your best tank, and the latter two are an excellent fire combo team, starting from turn 2 (you can even use Heating Up on turn 1 to speed things up if needed), while Diablo with the Black Soulstone can also take some hits, but you can mix and match depending on enemy colours.
As for the boss fight itself, you play your mercs in the following order (positioning is important because of cleave-like effects and those big fire missiles): Mutanus, Antonidas and Geddon. Mutanus will be heroically stalling with his Scaly Taunt until the bitter end, Antonidas will just trigger the fire combo for Geddon (yes, we just require his assistance) and take some hits for the team (beware the treasures that give your humans stat buffs! Antonidas is supposed to take the attack aimed at the lowest-health merc from the boss, otherwise Mutanus might fall prematurely… I’ve found it easier if Antonidas is the one with the lowest health total; of course, if your Mutanus also has stat buffs, then Elementary Studies might be useful, although not strictly necessary), while Geddon should be the one doing most of the damage, especially to the red ‘ads’. Your goal is to keep Geddon up and running with Inferno for as long as possible to do as much damage as you can. Once, for example, Antonidas falls, you can bring in Balinda with the elemental (remember to use clever positioning and protect Geddon from cleaves and big fire missiles as long as you can!) to keep the combo running. At some point Rogers + Diablo is your finisher, just make sure that the Fire Stomp kills all the red guys, so do not use up these mercs prematurely. Once Drek’Thar is alone (a typical orc and a Horde guy, brave only behind the backs of his goons and a weak coward without any honour on his own 
), he should fall quickly to your remaining mercs (like Diablo) without any problems.
Overall, both the climb and the boss require some thinking and planning, but, if played properly, you should be able to even farm the boss like this rather consistently, unless something has changed drastically (and, AFAIK, the only significant change has been the player always winning speed ties, which should make this even more consistent). Of course, there is always the danger of rolling unfortunate opponents on the map, and you cannot really afford to lose mercs before the boss on this one, but if you get really unlucky, you might just re-roll.
As for ‘nobody’ doing heroics, well, I actually prefer to farm them in order to make this somewhat challenging and meaningful for myself, rather then mindlessly grinding the heroic 1-1 instead, which is just extremely boring (besides, the coin gain for other mercenaries from high-level bounties, as opposed to the 1-1, might be advantageous for a F2P player in the long term, even though farming the infamous quilboar might be faster to upgrade a single particular mercenary). I understand, however, that while the developers would wish for other players to do so as well, the incentive for this is not always sufficient for many.
As for sentences like this:
Admittedly, there are a few heroic bounties that require specific mercenary combinations to solve them, and they are rather demanding on the player’s collection (infamously, Rend Blackhand and Drek’Thar are some of the most prominent examples, with some other bosses e.g. in the Blackrock Mountain also counting to a lesser extent), and currently there is probably one that qualifies as outright ludicrously designed (Kresh), but a lot of the others can be solved even ‘on a budget’ and, on the contrary, require strategy and planning (a separate issue is that some of them take a long time to complete, e.g. Omokk or Onyxia, but that’s another story). However, straining one’s brain even a little has apparently not been as popular amongst the ‘broader community’ of this game as it could have been for as long as I remember, alas. While I acknowledge that people have the right to seek instant gratification without thinking the way they please, including netdecking and so forth, and I have nothing against it, I dismiss such criticism as valid for the design of many (but not all, see some examples above) heroic bounties, which arguably have some depth to them as strategic exercises or puzzles (even though the Sunken City tends towards quantity over quality in that regard, if you ask me). In this light, my sympathies lie mostly with the players who are frustrated because their limited collection does not allow them to complete certain bounties, rather than those who just complain because they simply can’t be bothered to exercise their intellect a bit and yet bad-mouth not only the game design unfairly, but also, reportedly, even content-makers who are actually publishing detailed guides to help them solve the problem of these bounties.