The problem with level drain wasn't that it was a consequence. It was that, as consequences go, it was
boring. It essentially undid your progress with effects that were numerical and only changed how you interacted with the world if they took away spells. And it didn't even make your character
look more interesting.
Compare to losing either an eye or a hand. Rather than losing numbers and progress you lose a specific capability. It changes how you interact with the world. You then get to use a hook, an eyepatch, a glass eye, or even gnarly magical cybernetics. Your character and how they interact with the world is changed.
This opens two other cans of worms, both of which are best illustrated by 3.X:
- A whole lot of the broken stuff in 3.0 or 3.5 was in the PHB. A PHB only "Batman" debuff wizard with a good spell selection and a loose leaf ring binder full of scrolls is a Tier 1 character and one of the strongest characters in the game regardless of which splats you add.
- Known strategy and knowledge of the meta changes over time. Even if you stick to the PHB only and make a very mediocre fighter with the weapon specialisation feats and great cleave's contribution changes
- In 2000 the classic party would have been a 2e style Evoker Wizard, Healing Cleric, and Trapfinding Rogue. The fighter can keep up here.
- In 2008 it's much more likely that they get a "Batman" wizard (either conjuration or divination specialist, dropping evocation entirely), a self-buffing cleric who uses wands of cure light wounds for the party's healing needs, and an aggressively hegmonizing ursine swarm (a druid with a bear companion who turns into a bear and summons more bears) and if traps are a major thing someone has a single rogue level, taking one for the team. The fighter is fairly redundant here.
Has there been power creep? Both are PHB only, and some of the most egregious spells like haste were nerfed. As from memory was some self-buffing.