In my opinion HP is less important than Con save bonuses for Concentration-favoring spellcasters, even while gaining HP is a very valuable thing. That +1 Con save easily outpaces the value of Durable.
And for those characters they have War Caster or just a +2 Con. Toughness is not the feat for them....and there is absolutely nothing wrong with that. But for everyone else, 2 HP per level is too much.
I feel like characters should be able to excel at their niche skills. I don't think a Rogue or Bard should be strictly better than all Wizards at Arcana, for example. I'm ok with them being phenomenal at a whole bunch of skills, but being strictly the best at every skill they try seems out of place to me. That's why I favored giving access to advantage or expertise in this feat.
I think this is where you have to decide if you are making this list for you, or for a general audience. Core 5e says that Rogues and Bards are the skill masters, and are in fact better than all Wizards at Arcana. Now if you want to change that for your game that is fair game, but there are those in the general audience that see no need to remove niche protection. Certain classes are just good at certain things, and a single feat should not undo that.
Now I think you have some leverage with your specialized feats...because the whole point of the feat is to make you very good at a very specific thing. I think most people will get behind that. But giving away what is effectively a key class ability only a general feat I think is pushing it too far.