Retrospectively stripping of honours is pointless. Winning trophies is about the feeling and emotion of the time. Nobody's punching the air or starting an impromptu street celebration finding out that they've retrospectively been awarded the FA Cup several years ago.
It would be the same feeling a young fan researching their club discovering the honours they won in the 1950s on Wikipedia.
"Oh. Right" would be the extent of the impact
It's not pointless. It breaks the business model. Fewer State-sponsored regimes will go through 15 years of corruption and money laundering to circumvent FFP if it is meaningless at the end.
It deters the wrongdoing as there's less of an end gain. If City continue obstructing the PL investigation for a few more years (as done since 2018) and are then allowed to keep "their" trophies, fans will assume no wrongdoing.
UEFA found they had used corruption, financial doping and money laundering but because the sanction was suspended and financial only in the end, City have claimed to have been "proven innocent".
The punishment has to match the premeditated and determined nature of their aggressive corruption which has undermined the integrity of European football.