I think the idea of one chance stems from a different era in sports, when managers didn't get fired after just two or three years. Of course, now GMs also get fired after just two or three years.
Honestly I can't blame Dombrowski for much. The Phillies are historically a badly run organization, and they were especially badly run in the years between Gilick and Dombrowski, including Gillick's own brief second tenure. Monty's death was both an extenuating circumstance and inciting incident for the team to do better. Remember when they almost decided to go without a GM at all in 2020? Had DD not seen Nashville fall through, and had he not been a MacPhail crony, that might have still happened.
Also incredibly good luck that Middleton made a bad managerial hire (technically Klentak was still the GM when that happened) but Kapler's bench coach stuck around and proved to be a good one.
It would be interesting to see what Mattingly might do as his own man. Just as much risk to bring in any other candidate of similar age/experience. Hopefully they don't start thinking they need another guy with tons of experience. I'm not sure there are many viable candidates of Dombrowski's generation left at this point (let alone MacPhail or Gillick's).