I think you're making up a narrative in your head to support your bias against Disney here.

TASM 1 was definitely well received when it was released. It was tarnished by the slop that was TASM 2, which lead to Sony being able to come to a licensing agreement with Marvel Studios, to use Spider-Man in the MCU. I think it's an extreme stretch to think Disney had any nefarious doings in the public opinion of those movies, Sony did that to themselves and has proven time-and-time again they cannot make a good quality movie with their Spider-Man IPs.

The Rise of Skywalker is at 51% on Rotten Tomatoes, that was universally acknowledged to be terrible, even by the "critics". Disney definitely was also not able to silence or drown-out the absolute outrage by the cast and fans of the treatment of Luke in The Last Jedi.

Why would Marvel / Disney spend any effort sabotaging the DCEU when Warner Bros. was good at doing it all themselves? If Marvel was worried about DC stealing their audience, they would have focused more on movies like The Batman, not some c-grade antihero most people have no idea about? The Rock fostered a lot of the ill-will towards that movie himself.

I say all this but I also think it's accurate still to say reviews are trustworthy but I don't think they ever have been. I don't think this is some new phenomenon, just people are more aware of the corruption embedded in the system.