That's true though of its other mechanics and older editions though. Spell prep looks like Vancian, but it's nothing like AD&D or 3e. Multi-classing isn't like 3e despite similar design. Feats and ASI don't work like 3e or 4e. 5e never promised faithful translation of specific mechanics, only that it would take inspiration from the past in design.
Actually, in that post, I argued that feats are one of the few things that really are pretty much identical, up to the level of change necessarily induced by being a different game. 5e feats are
more similar to 4e feats than to 3e ones, let alone previous games, and it's one of 5e's great strengths that it preserved that aspect of the game, with feats that are actually interesting and flavorful.
ASIs, on the other hand, I will absolutely grant you--they work nothing like 4e, and it's a shame they don't, because 5e has a lot of really cool feats most characters will never see because they aren't anywhere near as powerful as +2 to your main stat....and most of the ones that are that powerful are incredibly boring math bonuses with no flavor or character to them.
There is a great deal of difference between "take inspiration from" (which, to me, means preserving the
spirit of the rules) and merely wearing the skin of older mechanics while literally being diametrically opposite in actual function. Hit Dice are diametrically opposite Healing Surges. They are a nice cushion of bonus healing on top of the critical necessity for magical spellcasting-based healing (or potions, which are magical anyway.) Cantrips are not at-wills, they are not even trying to capture what at-wills did; they are purely a power-up for spellcasters so they feel less punished for not casting proper spells every single round. Proficiency is probably the worst culprit, because its disguise is very, very good, but it negates the spirit of the rule it is allegedly inspired by almost as badly as HD do: Proficiency effectively
punishes anything you aren't good at, because that punishment get worse over time, very literally the negation of the spirit of 4e's half-level bonus.
Taking inspiration from something requires that you actually respect what purpose that thing was for. 5e mechanics do not do that with 4e. In almost all cases--feats being a rare exception--if a 5e mechanic resembles a 4e one, it actively negates whatever purpose 4e put it toward. Often, IMO, to the game's detriment; consider how many think-pieces we've had about how difficult it is to actually threaten PCs, how easy it is to get healing, the nigh-endless threads for the first several years about fixing saving throws because people weren't getting enough proficiencies, etc., etc.
Meanwhile, if something is borrowed from 3e, its spirit is preserved to the hilt--and often its mechanical implementation as well, often to 5e's detriment. The CR system is straight from 3e, and is equally garbage. Multiclassing is essentially identical, apart from ability score prerequisites--you claim it is in some way different but it barely differs at all. In a laundry list of ways, 5e is effectively a tweaked clone of 3e, not a radically different game. Hell, Extra Attack is already in spirit a strong resemblance to 3e's iterative attacks, despite being dramatically simplified.