Most joinery is in compression and hardly needs to be peg. Let's not forget draw bored holes are not all equal, a tapered peg allows for just the right snugness needed to pull the joint together during raising. If you have a 3/4 inch peg hole and a rived octagonal peg the corners will be larger than the 3/4 and will dig into the round bore hole of the mortice, in effect causing it to wedge the tenon and risking blowing out the relish on the back, if driven too hard.

Many old pegs I see are a standard size with little taper and a sharp point hacked on the end. I find this odd in comparison to my preferred longer tapered pegs.

I have no concerns with strength of a tapered peg. On true tension joinery the scale of the joinery is increased, larger hole, longer relish at the ends and perhaps an added wedge. Much different than your typical post, girt or brace joinery. My pegs in this case are still tapered but not as much.

A video showing a tapered peg. It is nice to be able to go through the box of pegs and select just the right peg for the drawn peg hole, they vary in size. Notice the size difference and amount of taper. My daughter just watched this and said " oh, that is a lot of taper" .
https://www.youtube.com/watch?v=-T-txHEaSoQ