LOL. I always shake my head when folks say this.
Hrm, 2 step recovery system, every class is built on the same model, instead of powers, nearly every class gets spells, many of which do the same things that powers did in 4e, skill system that is virtually identical (strip out the level adjustments from 4e and you get the 5e skill system), What else... oh, removing the need for magic items - 4e used inherent bonuses, 5e just does without, umm, what else?
You're not wrong about those being similarities, but they're not identical, and the play dynamic they generate can be /very/ different.
The short/long rest distinction in 5e, for instance, is 1 vs 8 hrs, often time enough for one is time enough for the other, you just can't take more than one of the latter in a given 24 hr period - the design assumption is 2-3 short rest & 6-8 encounters per long rest, or about a short rest every-other encounter.
In 4e the short rest is 5 min, virtually guaranteed between encounters.
The latter is a much more practical assumption to design around.
And, it's further complicated by the differences in class design. In 4e, AEDU classes were all on the same schedule, a variation in encounters:short rests:long rests impacted all classes about the same. In 5e, while, if you look under the hood, and listen carefully to some things Mearls has said, yes, there's an underlying spell-based design framework, the resultant classes vary wildly in the proportions & powers of their resources that recharge with each type of rest, which means varying from the 6-8:2-3:1 assumption alters class balance... not that classes are balanced to begin with, nor that they balance at that same point dependably as the game progresses in level (LFQW).
NPC's and PC's built on different rules, no magic item economy, spells attack stats, I'm sure I could come up with more.
So, /only/ 3.x of all the D&D species, built PCs & NPCs/monsters on exactly the same rules by default. It was always an option in all the others, but the presentation of monsters/NPCs in completely different blocks is the norm for D&D, just one of the few ways that 4e was normative D&D.
4e had a very prescriptive wealth/buy magic item economy, just like 3e. It was simpler to do away with it, but it was there by default and assumed. 5e nominally assumes no items (first time in D&D history, BTW, one of the few unique things about it), but no 3.5 make/buy, it goes back to old-school exclusively-DM-curated items.
Linking spell effectiveness - saves are mathematically identical to attack rolls - dates to 3.0, at the latest, and linking caster effectiveness to one stat goes back to the beginning. Using the same stat for the formal distinction of an attack roll as well as saves is almost trivial, really.
Having played and run both for about equal numbers of years, I can honestly say that if you think they're worlds apart and that 5e is closer to 3e, well, I'm not sure what you're looking at.
4e and 5e and 3e and TSR-era D&D are definitely worlds apart. Yes, even though they're worlds made of all the same elements in very closely similar proportions. Like, Mars and Venus are both terrestrial nickel-iron-core planets in the life zone - but surface conditions vary between the two. The play experience of 5e is - OK, can be - entirely different from 3e or 4e. (In all eds of D&D, the DM can greatly influence the play experience, of course.)
But, yeah, we're going to have to agree to disagree here. You see these massive differences in play and I simply don't. 4e and 5e, outside of combat, play virtually identically. 5e, to me, is just sped up 4e. It's an improvement, to be sure, but, the 4e DNA is most certainly there in every aspect of 5e.
The DNA is certainly there in all d20/WotC eds... the same base-pairs, 98-99% identical like Humans, Chimps and Gorillas - and at least as different as humans, chimps and gorillas.
I mean, your not wrong: D&D has stayed the same much more than it's changed - even with 4e - but among versions of D&D, 4e is the outlier along a lot more dimensions than 5e. And, in some of the most important ones, like the role of the DM, 3e & 4e are both more deviant than 5e.
