I totally get it. You don’t want more stuff or unnecessary expense and wonder if you can make it work with what you already have. Sure, a wetsuit and booties might double as a pair of waders, in the same way that you could frame a house and drive nails with a pipe wrench instead of a hammer. It will get the job done but not near as easily or efficiently or enjoyably.
My thoughts:
With a properly fitted wading belt, waders offer buoyancy and will not completely fill with water
It’s nice to be dry after a day of fishing and not wet
Waders are easier to get in and out of than a full body wet suit
A good pair of wading boots offers a higher degree of support and safety when wading than booties.
Waders are good in all seasons. I don’t see wetsuits being practical for fishing when the temps are mild/warm
If your style of fishing is standing in one spot all day, then a wetsuit might work. If your style of fishing involves a lot of hiking and movement, then the breathability and fit of modern Gortex waders shines.
Cheers