Yes I agree its not the weight its the way you carry it. I always take a back pack with at least two bottles of water, extra battery, cards, cleaning cloths, glasses, short lens, filters, I can put a five pound lens in there and carry it for many hours with no problem. I never use the strap any more unless its walking to the car. have found that a medium tripod moved shoulder to shoulder is the most comfortable way to carry my D810 w/long lens, (even better than a monopod) but most birds/Bobcats/Deer/coyotes/Cougars/and other wildlife just won't wait for me to put a lens on my camera and shoot.
Thank you, Bob W.
I think you've captured the dilemma hikers face... I can carry my D810 and 300f2.8 (or 200-500) on mountain trails as long as it stays in the backpack. Problem is - in the few seconds it takes to dig the camera out of the pack - the wildlife/ideal shot is gone! If photo opps of wildlife are abundant - but fleeting - the only solution is to have the camera in the hand, ready to shoot. Not sure of the wilderness trail conditions in so. California, but having a largish kit in the hand on mountain trails here on Oahu is asking for trouble, and will slow me down to a crawl to protect both equipment and myself

One solution is to carry two systems - FX and CX. FX in the pack until you come upon a photo opp that you're willing to stop and break it out; CX in the hand while you're hiking. Thankfully, the CX kit adds little weight (31 oz for V3+70-300CX). A couple of earlier posters suggested a V2 - I've used a V3 with wide zoom (6.7~13mm) and 70-300CX for tele that worked well. Of course, if the trail is really long, steep, or hazardous...I'll probably leave the FX kit at home (still gotta carry lunch, water, first aid, phone, rainjacket, et al, after all...).
Roy