I think it is reasonable that Mauricio Pochettino has not been able to fulfill his promise because Chelsea did experience a serious decline in the previous season and the coach also needs time to be able to fulfill what is expected and since the time he took office as Chelsea coach he has improved Chelsea's performance and managed to finish better than the previous season, even though his contract at that time lasted 2 years if Todd Boehly had been more patient, Chelsea could have been in the top 3 in his second season, unfortunately the club was not that patient and they fired Pochettino at the end of the season.
Honestly, if Chelsea's owner had been patient enough with Pochettino, Chelsea's performance might have improved significantly based on the improvements we witnessed towards the end of the season. I did not really expect that Pochettino should be sacked last season given his performance. Pochettino made Chelsea recover their performances, despite it not being as expected. Let's see what the new manager will do; maybe Chelsea's performances will improve as we expect next season.For now, I can't really say that the new head coach will be better than Pochettino, but if Chelsea's performance does not improve as much as fans expect, it will be regrettable to have sacked Pochettino. I just hope the new manager performs better than Pochettino.
Poch would have still remain blues coach till now if not for the unknown issues he had with Todd during their meeting that brought his sudden sack even when we fans were chanting for Todd Boehly's to sack him, he gave deaf ears which was a proof that he really wanted him for a Long term before all the drama happened and now we have Enzo Maresca's as the new head coach.