My wife and I were on a day trip today. We were driving down back roads in our province...curvy roads, up and down hills like a rollercoaster, narrow in width, lined with forests and a small river running parallel with the road. Great trip. I took my K1 and 28-105 and my K5 with the Sigma 150-500. I like to take this equipment as I'm ready for anything I may see. Missed out on a photo of a Bald Eagle close by...but spent about an hour in a salvage yard with many very old automobiles in a salvage yard. I was glad I had my K1 and 28-105. I wandered around with this unit...also has the battery grip with an extra battery installed...for about an hour. Up and down steep inclines...must of walked about a mile or so...bending down for different angles, etc.
I'm no spring chicken...at 69...but I wasn't really all that tired hauling around the K1 and lens....and I really enjoy having the K1 full frame...lot's of margin for cropping, etc.
The K5, also with extra battery and battery grip...attached to the 150-500 isn't a lightweight, but I do carry around that combo in a semi regular basis going down forest trails.
I'm not Superman, not by a long shot
...but although I admit that this camera (both) equipment ain't light...I can still carry it around without too much difficulty and do so...on a regular basis. The image quality I've got from both combos ...I find just great. I have no plans to change anytime soon. Maybe in another 5-10 years when I get more elderly I'll want something lighter...who knows .
But then I'll take my small, lightweight Pentax Km/K2000 body with the lightweight 21mm Limited and my old, reliable 55-300. A lighter, smaller package that should be almost perfect as my old body 'seniors'...
I don't know how much lighter or smaller my Km/21 Ltd... is compared to the latest Fuji mirrorless...with lens...but I would be surprised if there is a great difference. I dunno, I bought my Km new in 2009...maybe Pentax was ahead of the pack with light, small cameras.
BTW, the Pentax Km uses a ASP-C sensor (think it is only around 10+ MPs) and the pix are great IMHO. I know it's old technology, obsolete, no new and improved factor, etc., etc...but other than those disadvantages it works real well. Ahh.... what to do ?