Actually, with the task system’s rework, that might be more player-friendly again (the problem was that a task chain for a particular mercenary was hard to come by, even more so after the chance to get the Mysterious Stranger was reduced in 23.0) — although that’s up for discussion, maybe it’s still more fun the way it is now. Some equipment is locked behind bounties that can be difficult to do on a ‘budget’ (or used to be) — although it’s not that bad nowadays: you can do a lot with Cariel-Xyrella-Samuro, you can farm coins for Malfurion and Anduin in Felwood to get some good parties (Nature and Holy) started, and these can take you even further… Garr is also an easier bounty that drops coins for Velen, in order to complete the ‘classic’ holy team, and Jaina to build a ‘budget’ version of the Frost party without Balinda consisting of Jaina, Varden and Lokholar — the best equipment for the latter is available at level 30, by the way, and not locked behind a Heroic bounty. As soon as you complete Winterspring, you can go to Alterac and proceed on Normal, there you need to defeat Heroic Rotimer, which isn’t that bad, for Yu’lon’s equipment and thus complete your ‘budget-Dragon’ party (Yu’lon, Sinestra and Nefarian, for starters — and these are probably among the strongest of the dragons anyway)… Even if you don’t feel like grinding for legendary coins, you can do a lot with only rare mercenaries such as Trigore, Lokholar, budget Dragons/Nature and so on.
Not sure if I could agree with you. The coin exchange system is probably there for those stubborn mercs that are hard to max after completing their task chains (I’m not taking the infamous quilboar into consideration), due to the way their coins are dropped, for instance. The main way to upgrade mercs should be doing tasks and running some bounties, and coin exchange should probably be there to complement this system, not replace it entirely — besides, right now new zones tend to drop coins exclusively for newer mercs, so doing these (on whichever difficulty you prefer) would make sense in terms of rewards, at least until you upgrade most of them. After that point you usually have a few stragglers left, which is where the coin exchange would come in handy — assuming it’s done right, which remains to be seen yet. Even if it would be a couple of offers per day, the small assortment of potential candidates — as it tends to be the case for more or less active players — would ensure that you would generally get the offers you need, more or less.
(Some edits made)