Too many variants like this are designed to screw with the casters, but what about those who hit things with a sword?
I propose if you're going with Gritty Realism and limiting healing magic, you also insist on applying disadvantage on all attacks when a character is under 50% hit points, to signify that the wounds actually have an effect. This would limit spellcasters to some extent, but they could choose to rely on saving throw spells as well meaning it hits your barbarians, monks and fighters the most.
As for the idea behind a low-magic world, how do you manage to say "low magic" then say "fighting a dragon" in the same breath, surely a dragon wouldn't be allowed in a low-magic world?
I agree too many classes now get spells for the sake of it, I mean Paladins and Rangers don't really need their spells in the slightest, they could've covered 90% of their lists with supernatural abilities (and Eldritch Knight/Arcane Trickster could've been given per day spells as well instead of spell slots) and the other 10% is longstrider and crusader's mantle!
Ultimately when you design your low magic world, consider being fair to all players in how you restrict things. If you ruled out classes with any magic you're left with a Barbarian, 2/3rds of the fighter, Monks and Rogues which doesn't really leave a lot to play with. I don't think I'd go with a low magic world unless someone created non-caster Bards, Paladins and Rangers to give people more options.