I was there Thursday through Monday, and honestly the crowds weren't nearly as bad as I anticipated they'd be, even on the worst days. Guardians had crazy long lines (to be expected) but the rest of the park was manageable for the entirety of my trip.
Thursday (for whatever crazy reason) was actually one of the most crowded days, focused on
Disneyland Thursday, but I used my Magic Morning that day and got a lot done early. Had a few 20-30 min queues later, but nothing too bad.
Friday was an absolute breeze. I walked on all the smaller rides at DCA, while fastpassing or single riding the bigger ones. But did just about everything in the park. I think my longest wait all day was about 20 minutes for funwheel. Got basically everything in the park done before 4 o'clock. (Including the lame rides in bugs land and paradise pier, haha)
Saturday was similar to Friday if not better. Walked onto many of the big ticket rides at DCA and Disneyland.
Sunday wasn't as good as Saturday, but still manageable. Monday was much the same. I was honestly expecting horrible holiday crowds (especially after reports they hit capacity the weekend before last) but was pleasantly surprised by how manageable it was. Some days were downright good. No crowds. Minimal waits. Even when it backed up more, as long as you did the big stuff early and juggled fastpasses effectively, it was all doable.
The ONLY thing I'd call a nightmare crowd was Guardians, and even that was manageable. Got there early. Secured a fastpass. Rode it in the afternoon with no wait. (I would not touch standby on this ride with a 30 foot pole however until the hype dies down). Pretty sure most of the DCA crowd was being absorbed by this ride, leaving other things less crowded all weekend.