I’ve not delved into the details of the differences between versions - my interest in PRO is that it offers a lot of stuff that Platinum didn’t tho - such as
Supports the myriad plugins out there - there are literally millions of them
Supports proper masking (Platinum only supports fixed and limited shaped cookie-cutter regions)
Every tutorial you find (and there’s millions) seems to assume you have PRO - I guess everyone pirated PRO ;0
As for whether it’s overkill - at $20 your only alternatives are free packages like KDEnlive or (MS) Movie Maker with the former “forever Beta” and the latter a shadow of what WMM once was??
p.s. someone on Reddit mentioned HitFilm Express which is new to me and free - you may find that interesting?