To a degree we were no worse yesterday than we have been of late but, as Celtic are possibly the best team just now, they ruthlessly exploited our weaknesses. Team selection again looked odd but we don't know if there are any fitness reasons behind it (Ojala for example). We're not the best side when not in possession as Celtic well knew.
There are also a few unknowns just now like the impact of players like Efford, Shaw and possibly Tierney.
We need to sort out all areas of the team; defence; midfield and up front. For me Slattery, Goss, and Cornelius are stick on starters in midfield if we play with 3 nominally up front. If we go with 2 up front then Tierney slots in between them and the 3 midfielders. I'll reserve judgement on Shaw for the time being.
Longer term, I would be in no rush to renew the contracts of Donnelly and O'Hara. Maguire is a squad player at best.