I wrote this in 2018. I was comparing a 25% 777 FO to 25% 757 CA. Those don’t quite line up anymore but most of this generally still applies without any added Covid factors. If I was in your shoes and I knew I could count on a bunch of free, paid days off at home on reserve maybe I’d consider it. But if you’re flying regularly and you’re looking for best QOL for the money earned, 757C isn’t where you want to be. If I’m going to accept all the responsibilities, especially if I’m working harder, then I want more money. Why would I accept more chance of diverts, C048 approaches, getting swept, 3 legs nights, AM hub turns, on and on and on. My last sim instructor for recurrent had recently done three C048 approaches in a 757 in one duty period. For the same or better money you can have one takeoff, one leg, an ILS (cat-3 autoland if necessary) and head to the hotel. Once in a while you get a couple of legs in a duty period.

The bottom line on this really comes down to credit hours per day of work. Doing a little bid pack kung fu using your favorite bidding software will make most of this readily evident. I'm certainly not interested in convincing someone senior to me that 777 FO is the place to be, but it's really not that difficult to figure out. There is way, way more to this than simply looking at pay rates.

June bidpacks for both seats:
Max days off lines on the 757 (17 days off) pay 68.1 CH or 6.2 CH per day. 3 international Trips. Comprised of 2 leg and 3 leg duty periods. You get 3 round trip commutes to do that (unless you want to kill the 2 dead days between trips in MEM) while flying 12 revenue flights that month.

Max days off line on the 777 (20 days off) pay 69.2 CH or 8.65 CH per day.
2 Trips as an RFO. Both two 2-day front deadheads to HKG, so two "half-commutes" on the back-end of each trip with a paid two day commute to start. One 15.5 hour revenue flight back to MEM each trip for a total of 2 revenue legs that month.

Do the math on those two lines and the 757 CA makes more that month. BUT - a very important BUT - he works 3-extra days to make those additional dollars.

Since the 25% 777 FO can consistently hold carryover, he can choose to plus up his month using a 3-day trip and work the same number of days as the 757 CA above. I'll be conservative and say those 3 extra days pay 6.4 (trip rig) per day. So now - working the same number of days as his 757 CA buddy, he earns 88.4 CH of pay for the month (averaging just over 8 CH of pay per day).

777 FO: $215/hour + $8/hour x 88.4 = $19,713 for the month

757 CA: $262/hour + $10/hour x 69.1 = $18,795 for the month

Pick a more middle of the road scenario: Find some lines with 16 days off each.

A nice two trip month on the 757 both with double deadheads:
68.5 CH of pay for the month (5.7 CH per day) - some nice layovers, only one two leg day on each trip, 8 revenue legs for the month.
68.6 x $262/hour = $17,947 for the month

Over on the 777 - a single double deadhead RFO trip for the month:
77.5 CH of pay + 6 CH of over 8 BKO for the month (7 CH per day) - Two-day deadhead to Asia, some nice layovers, one leg a day when you do fly, 3 revenue legs for the month.
83.5 x $215/hour + $8/hour = $18,621 for the month

The bottom line is the "Q" in QOL is subjective. That's the nice thing about FedEx. Lots of options.

Maybe someone can't stand being in an aircraft longer than 2-4 hours at a pop.
Maybe they can hold their hometown layovers.
Maybe they prefer LCA duties.
Maybe they hate riding on commercial aircraft.
Maybe they have reasons they can't spend 12 days gone all at once or just don't like that.
Or maybe they just gotta have those 4-stripes no matter what.

But if none of the above applies and a 2001 hire is working his ass off (relatively speaking) in the left seat of the 757, even at 25% instead of earning more per day as a 777 FO ..... I'll just say - better him than me.