As soon as you get outside amateur motorsports it stops getting done. And most other motorsports are using much thinner steels so it's generally the TMT that you see there, not this.
Most of the suspension components on those are overbuilt as hell to make up for it, and they'll have 4 yards of cold lap mig on a part attached by a couple of horizontal rose joints, so the welds aren't really the weak spot. FWIW one of the FSAE teams did a full analysis on a Trophy Truck...
Epoxy needs to be far, far more precise than polyester. Polyester hardener is just a catalyst to kick off a chain reaction, epoxy is two components reacting with each other
Depends what it is, nylon is a swine to glue to, welding to it is better, but PC/ABS which is common on bikes is fairly easily bonded to with almost anything.
Yes, and often when I've got sick of modern metal clamps not actually sealing properly I've cut them off and replaced 'em with cable ties and had no problems.
The racer gets cable ties too.
Depends how they do it, I've often seen it with just the usual single axle and shafts and then chain drive boxes to the paired wheel from the driven one.
Those will be faulty drives, that should never happen with anything reputable, because they have enough over-provisioning for the lifetime of the drive. I'm up to probably 50-100 SSDs and I've never had that.