I think Deila screwed up by not rotating last year, but I don't think we can say that's typical for him or predict he'll do the same going forward. Last year was so weird and unique. Besides the covid break, and the odd schedule, the team started 1-5-0 with just 2 goals in the first 6 games. Then Maxi goes out for 7 games, Heber for 10, Sands for 6 and Mitrita leaves with 8 left just as he started clicking and probably would have gotten more minutes with Maxi and Heber hurt. I think Deila kind of freaked out, and felt he had to just keep the gas pedal down with his best remaining players all the time. I'm not defending him by pointing this out, but I do think it's not predictive of how he normally will operate. Of course the 2021 roster is creating its own challenges. Not sure how he'll react if we're 3-8-2 before new players arrive and the first half players are burned out for reasons not of his doing.
Also, when he came, there were a lot of Celtic fans on twitter and such giving us all sorts of reports. Mostly they liked him personally and were kind of split on his coaching ability, but I don't remember once hearing that he ran his players ragged by failing to rotate, failing to make substitutions, etc. I think he just made some bad decisions under hopefully never-to-be-repeated conditions.