Nah I don’t think so.
I’m not your weight nor height but when I used to ride my Niner hard I had no problems at all with durability etc. But I have to qualify that by stating all the spangly bits on the bike are Niners RDO.
There are some right old lumps near me and I climb hard often honking up pulling the bars (side to side) ok they flex a little, but they’re supposed to right?
Downhill and I always wuss out so can’t comment on that.
But at Charlies SS event last year there were some right old chunky blokes having a whale of a time on rigid SS’ers and hacking past me on the downhills without a care in the world.
Can’t see the problem myself, buy some good quality spangly bits and you’ll be fine IMO.