I know, totally left field here but someone had to do it so might as well be me 😀 but would the Ronin RSC 2 not work for you? I know it is heavier and probably larger than you are looking for but at the end of the day no one comes close to DJI for reliability, stability, and performance. I've had a love/hate relationship with their gimbals for many years now. I started out on the original Zhyiun Crane; switched to DJI's Ronin S and have never went back. I now have the RS2 and there is nothing more that I could want out of a gimbal.
The thing is, your starting rig is pretty heavy, so putting a rig on a gimbal that is anywhere near its maximum payload is asking for trouble; the payload capacity could be overstated, the motors could simply die sooner, or you could just get jittery footage. The RSC 2's payload capacity is nearly 50% more than your planned payload so it will be able to handle everything you throw at it.
Every other gimbal maker feels like they are just trying to be as good as DJI (but failing) so for me I'd rather buy once and use for many years vs always looking for something "almost" as good as DJI.
As far as fatigue goes, you probably know all of these but there's many little tricks to reducing it. I stick the end of the gimbal into my belt anytime I am not shooting with it or have to stand for long periods of time, you can get a shoulder strap for them, there's even a shoulder strap mounting rig, etc. Working out helps greatly too, a few dumbbells and hammer curls each day will make your payload feel weightless and help with the fatigue within just a few weeks.
Also, I don't know your particular typical project, but for me I've pretty much ditched my gimbals altogether and really enjoy handheld. I only use gimbals when I need to walk or run with the talent or need complex camera movements. If you do a lot of interview type stuff you could try a monopod or even a shoulder ENG style setup which are all less stressful than a gimbal. Obviously if you are only shooting complex camera movement and need what a gimbal offers then a gimbal is your only option; but for me personally I have gotten much better with my handheld technique and the gimbal usually never leaves the bag.