Equally it's a modified version of 4e. Bounded accuracy; the lack of scaling spells; classes with "sub-classes"; its action economy; much of its approach to weapons and armour; etc, etc, etc.
Is it?
Subclasses already existed in PF1e as "archetypes", which themselves grew out of 3e's "Alternative Class Features" and the like. They're just prepackaged, something that runs through almost the entirety of 5e (e.g. Specialties were going to work that way, but had to be abandoned because they finally realized Specialties were a bad idea.)
No idea what you mean by "lack of scaling spells". 5e is full of spells that scale? And I'm not talking cantrips. Upcasting is a thing in 5e, which has literally no equivalent in 4e, but was in fact something you could often do in 3e.
The action economy is nearly identical between 3e, 4e, and 5e...and where 5e differs, it differs from both of them equally. 3e called them Standard, Swift, and Move actions. 4e called them Standard, Minor, and Move actions. 5e calls them Actions, Bonus Actions, and movement (not described as an action, but still functionally one). If anything, this is a point where 5e actually
does differ from the previous two games more than those two resemble each other: in both 3e and 4e, you had to spend your movement all at once, and couldn't do it "within" an action unless that action specifically merged your Standard and Move actions (e.g. Bull Rush). In 5e, your movement is something you just have at all times during your turn, and you can use it as you like. This, incidentally, was one of the things I was specifically thinking of when I said that the "chassis" remained more or less the same.
No idea where you're coming from with the weapons and armor thing. 5e weapons are vastly more like 3e weapons. They have no tags. They have
precious few special features, essentially all of which were in 3e, albeit sometimes done differently (e.g. "finesse" was a character feature in 3e, as opposed to a weapon property in 5e. It didn't exist in 4e--that was handled by the "Light Blade" weapon group, which as said, doesn't exist in 5e.) This is one of the few areas where I can speak pretty authoritatively, mostly because I attempted to reverse-engineer the weapon construction rules used to make 4e weapons. I think I have something that is at least more or less what the designers were doing. It's a
little bit of a cheat--glossing over a couple unusual exceptions and having to grant certain seemingly-valuable properties as being "free"
if specific other properties are present--but given at least some of these weapons were apparently notorious in the 4e community for being crap-awful trash (e.g. the ordinary club).
4e weapons genuinely have much more
design in them than 5e ones do. It's quite clear to me that 5e went back to the 3e weapon table, slimmed it down, and gave a
very slight nod to certain 4e ideas, without paying very careful attention to the details. That's why the 5.0 trident is a harder-to-use (martial vs simple), heavier (4 lb vs 3 lb), more expensive (5 gp vs 1 gp) spear...with otherwise completely identical stats. There is never any reason to use a trident in 5.0 when you could use a spear. It's worth noting, making the trident actually better than the spear is one of the changes 5.5e implemented (it now has one better damage die, d8/d10 versatile, and a different mastery property). And, on that subject, Mastery Properties
are quite clearly a design attempting to reconstruct the 4e weapon groups and their soft association with particular weapon properties (e.g. axes have Brutal N, swords have better accuracy, etc.), just comparatively clumsy, because they had to bolt it on after the fact rather than having the notion baked into the system from the start.
I'm about 90% finished with those aforementioned build-your-own weapons rules, incidentally. They should be usable even with 5.5e, though you probably would want to be careful about including
both these rules
and Mastery Properties, since those didn't exist when I started designing these rules.
