Pointing at new 5e books to make that point is like pointing at fridge magnets to support an arguement that there is room inside for a trunk full of groceriesBrevity is the soul of wit...
The suggestion that 5e isn’t modular (whatever you take that to mean) not only isn’t ‘slam dunked’ it isn’t even convincing.
The system is clearly modular - as evidenced by the many expansions released in its lifespan.
[Edited - rather than add a new post]