Don’t forget solo dungeons coming in 10.2.5, with help from NPCs. Just announced today:
Tank, heal, and DPS alongside follower NPC companions that join you on your Dungeon adventures. They will be available in all eight Normal Dragonflight Dungeons and can scale from 1–4 players. These companions will allow players to learn about Dragonflight dungeons at their own pace and provide the freedom to experiment and customize their Party makeup.
Anyway, best solo class …
You are right about Beast Mastery Hunter and Warlock with a Voidie. If nothing else, your tanking pet has 70% of your HP, which means that, effectively, you have an extra 70% health, plus healing abilities. That beats any other possible DPS spec.
I haven’t heard of any nerfs, (apart from a Hunter damage nerf recently to compensate for an unintended buff) but I am entirely sure that no possible nerf will be big enough to bring either of then down so much in survivability that any other DPS class can compete. Nerfs and Buffs come and go, but they will always be vastly more survivable that any non-pet DPS spec.
Also, with those two, you can stand at a distance and move around calmly while fighting, I have one Warlock, whom I rarely play, but in the past two expansions I’ve been speccing him Affliction and throwing instant DoTs from range while my Voidie takes care of business. It is without doubt the laziest I can be in the game.
Hunter also has the attraction (for me, at least) of selecting and acquiring pets as a sort of side-game.
Another thing you might consider is picking up a class with a Tank spec.
I have a Paladin who is formally both Retribution and Protection, but I have rarely moved him out of Prot for the past two or three expansions. I do love Prot Pala. Armor like a bank vault, endless self-healing, and just about every utility ability under the sun. Plus that glorious Avenging Wrath! And Avenger’s Shield is as near as you get to being Captain America.
You might think that running him in Prot would make for slow questing, but I find that’s not the case. Protadins have decent damage for tanks, and the ability to pull EVERY mob as far as you can reach and burn 'em down at the same time. With a HUGE pull, that adds up to more DPS even than my hunter or mage. It’s pretty much impossible to die as a Prot Pala.
Pala may not be the tank class for you, but there are others to consider. You can play both the Tank spec for survivability, and a DPS spec to cut through weaker enemies more quickly.
Warrior has a fun DPS spec in Fury, but Prot Warrior does have a weakness against big single targets, in that its main self-heal is triggered by the death of an enemy, and if you are hacking at one of the big rares that Blizzard has oversaturated the Dragonflight max-level world with instead of real content, it doesn’t help you much.
I know that Vengeance Demoin Hunter is a competent tank, but I always feel squishy by comparison in it.
Same for Brewmaster Monk, but that’s because I know I don’t like it - too many finicky auras and cooldowns, and I never gelled with the class at all.
I find Guardian Druid extremely simple and comfortable if you like being a bear, (which I don’t particularly) but I find it slow to kill things, even when I pull a big group.
Blood Death Knight is pleasantly inexorable, but also slow.
What is the difference between a pet class and a tank? In general, tanks can probably take down bigger rare-elites than pets can, and definitely do better with AoE pulls of large numbers of mobs, but sometimes having a pet can let you skirt mechanics that a tank can’t.
Anything else you want to know about them? Do please ask!
P.S It takes almost no time to get to about Level 40 these days, and by 40 you do have a general feel for how the class will handle later. You might consider investing a couple of days here and there into taking a couple of these for a test drive!