Bedrockgames
I post in the voice of Christopher Walken
In comparison to the TSR editions, the WotC editions have very limited space for kitbashing without affecting the foundational core, thanks (no thanks) to the WotC designers having gone the unified design route rather than discrete subsystems.
In 1e I can rip out entire subsystems and replace them with something different without (usually) too many knock-on effects to the rest of the game. I know this because I've done it.
Not possible with any of the WotC editions, as a major change to the design here is inevitably going to cause knock-on effects everywhere else; it's more work than it's worth to go and find them all and stamp them out, and doing so can simply cause the knock-ons to cascade in any case.
I do think TSR era stuff was very easy to kit bash, partly because so much of the system was not integrated into a core mechanic (so it just made it easier). I will say one feature of 3E I liked, was how much you could kludge using the multi class system. Unbound, it it was an optimizer's dream, but if you cobbled them together from different books selectively, you could really make some interesting setting options.