Whilst Stoll saved the team a few years ago, he made some decisions which have contributed to what happened this year, by deciding to ignore the engineering team and deciding that copying everything that Mercedes did was the best way forwards. That worked for Racing Point in 2020, but there were consequences for future cars when the rules change.
For the 2020 season the Racing Point engineering team wanted to continue to work on the high rake car as in their view, it had greater aero performance capability. But Stroll wanted the low rake Merc concept on the Aston so the aero team had to change approach completely.
Being able to copy an existing car with constant aero rules worked very well for 2020. But worked badly in 2021 where the rule changes, as you have overviewed, impacted much more on low rake cars. As the Aston aero team had not been developing the low rake car for years and years, they were always going to struggle to find a solution to their aero problems, and finished 7th.
As a side note, it is clear that high or low rake aero can work, but as an aero team, you need to fully understand your approach, just copying another team leaves you in a weak position when the rules change.