My view on signing the fitness for duty statement on the release is that you'll be good to operate the entirety of the flight including any non-normals that may arise. I've had a few cases in my career where I took off thinking I was good and 4 hours in it felt like being slapped by a bag of bricks. My takeaway from those situations is that I shouldn't have pushed it and should have called out fatigued before beginning that flight.
We can sit here and argue the turnback vs continue decision and we all have different comfort and experience levels flying without autothrottles, but ultimately that's not going to garner much criticism at the end of the day since the outcome of the flight was positive. What's getting criticized is once that decision has been made, there's no need to dance around it and try to get the company to arrive to the same conclusion. You already have the premises to return due to a mechanical, tell them and act on your decision. Fatigue might have played into your decision but the official reason is mechanical.
What's even stranger about this lack of assertiveness is I've never had SJI even remotely push back on similar decisions, so I'm not sure where the fear of confrontation comes from. I've had to turn a 767 around because one of the packs went crazy blowing full hot air in the cabin, overheated, and tripped. We couldn't recover it in either auto or standby modes per the QRH. Further troubleshooting over ATL radio with MX didn't fix it, so I told the dispatcher "hey I know theater restrictions are for dispatch purposes and there's nothing in the QRH saying we have to land, but I don't think it's a good idea to cross an ocean on a single pack and we don't feel comfortable doing it". He said "totally agree, let me see if there's any airport with spare planes and crews that would make the recovery easier otherwise let's go ahead and turn around". I've also refused to keep flying an airplane after an issue that was noted as intermittent on an "info only" writeup turned out to be a much bigger deal, and they simply said "sure there's another one pulling in a few gates down the concourse, head over there and I'll send you a new release". Nobody ever fought me so I don't see why he was hesitant to make the call.