I think it could make a difference, and if it does it’s not about the addition in work load but the rest days taken away. If adding 25 days of work during a season halves your 50 resting days it is huge.
Let’s say a normal person works 260d/yr, and goes up to 300d/yr instead, a similar increase, which means you have to work Saturdays all year, which kind of sucks if you’re used to having the whole weekend off.
Not that I know how much these overpaid lads slack in a week anyway lol but I think the reason so many foreign managers come here and complain in interviews about the schedule and work load and winter breaks and days between games and whatnot, is rather the lack of rest days. Especially if they have to rotate, play their potato players for a few games and don’t get the three points. And it is quite common for teams to perform better when in fewer cups.