OK, let's start from a common point. What do you consider the engine of D&D? I don't really think I can discuss this with you without understanding where you are coming from. Then we can discuss.
A few other comments...
Whereas to me, this is all how the engine is applied, not the engine itself. Progress rates are just bounded accuracy minus the rising number - the end result is exactly the same, a success rate of about 66% most of the time on most checks.
that completely misses the point of BA and its difference to 4e or 3e for that matter (and is also inaccurate for 5e at least).
Roles are very much still there. They just aren't called out.
They were there before 4e too, but 4e treated them a bit differently. 5e goes back to the pre-4e method. That is point.
Granted, tactical combat is much less of a thing in 5e, simply because 5e has combat that is so much shorter than 4e.
That is a part of it, but it misses the point that so many of the 4e powers did something more than damage (push, pull, inflict a condition, etc.). That is what made it tactical, not to mention the synergies between characters. If you think it is just combat length, then I think you missed a lot. I mean I can easily make a 5e combat last 5, 10, or more rounds. But I can't make a 5e character have the in print tactical options a 4e character has.
Paths and Destinies were never really important.
To some sure, to others they were.
And, stacking bonuses were, again, simply how the engine was applied.
Not sure what you mean, but it is different from 5e in that regard.
No, nothing really close (except casters) to what 4e had.
Unified structure? Well, we got three now instead of 1, but, still mostly the same - and, after 3rd level, every class advances at exactly the same rate.
Not the same, really at all.
Like I said, to me, none of these things were all that important to 4e. They were how the rules were applied once you had certain assumptions - the assumption of longer combats, for example, meant that healing surges and tactical combat was more of a thing.
You deal realize Healing Surges, and the integration into the core of 4e, are fundamentally different from HD healing and healing in general in 5e?
Remove longer combats (how the rules are applied) and there's no longer a need for these.
There was never a need for them, it just how they built the game. And just making 5e longer does not do anything accommodate healing surges and how they actually limited healing.
But, you still have two step recovery, at-will, encounter and daily resources, although they aren't called that, so on and so forth.
Yes and now. Again, 4e was a unified design to a level that doesn't exist in 5e. And simple because you have some things that are similar, doesn't mean they are the same "engine" IMO. Of course, I have realized I have no idea what you mean by "engine." I hope you can clarify.
