I started building my own ebikes with rear hub kits back in 2012. The experience of building your own ebikes is invaluable and somewhat addictive, too.
By 2014, I was building 45 mph capable hub-drive ebikes from my downhill bikes with suspension & brakes that can actually handle the extra stress of traveling at higher speeds (on or off-pavement).
I've also built ebikes with BBSHD kits, but ultimately I don't find it provide much more advantage than hub-motor for my application.
I've sold all the ebikes I've converted and I'm glad that I did while they were valued and appreciated.
Fast forward 10 years to today, I find the "need for speed" or "more power" overrated,
Yes, it is fun to have 1000w available with a twist of a throttle, but that seems to get old rather quickly to me.
On pavement, fast ebikes tend to attract attention from law enforcement (& thieves); off-pavement, I would likely get myself into hospital (during a pandemic).
I think everyone can benefit from a bit more mobility, ebikes can provide that with ease; at times far more capability than needed for original purpose for an ebike.
IME, one can save money & time by buying a complete ebike & spend more time riding instead of researching & building .
Whichever you decide to pursue; I wish you the best.