I agree that especially at higher levels, the time commitment (scrimming 2hrs+ every day) is often draining. Add in mgeing/jump maps or whatever you do to practice before scrims and it can be such a large chunk of time you have to dedicate to TF2.
However, I also really doubt the cups are the answer either. Everyone always says they want cups, that they'll play them, but after the 2nd one, people rarely sign up. I remember Essentials used to do a monthly cup that had 1000$ prize (it may have been more or less, I can't quite remember) but after 3 there were only like 8 teams signing up. FaceIT had something similar and people were barely signing up for them. I don't think there's been a case of a regular, consistent cup series having a regular/consistent signup amount, which probably makes it hard for organizers to accurately create good schedules.
The schedules themselves are often equally draining as well. You might be playing 4+ hours of TF2, interspersed with an hour to 2hr wait in between, where the whole schedule can get delayed from one match/team. Maybe the answer is multi-day cups, you play a group bracket during the week and then playoffs on the weekend, but at that point, it just starts looking more and more like a shortened season.
Additionally, the skill disparity (even in cases where invite is separated) is often so gigantic that most matches are 5-0 rolls. And when the signup rate is low, as it seemingly inevitably will be, that discourages lower-level teams, cause they'll know they'll get steamrolled by whatever adv/main team that's playing.
I'm not saying cups aren't good or can't be fun, but they have not proven themselves to be a good replacement for seasons at all.