-Cena's run started in 05' and his first reign was wildly successful compared to the shytshow that was 03 and 04 for the WWE. There is revisionist history because at the time, Cena's metrics were compared to 98'-01' WWF which was the biggest drawing run any promotion ever had
so they were never that highly praised. But as time went on, his initial run was great boost for business (Batista as the 1B guy was low key important too).
-His run wasn't the lowest attendance or lowest ratings in WWF/E history, what the fukk
shyt, before Roman turned heel and the Bloodline storyline started to gain momentum, that period was really bad attendance wise, and the company isn't running half the shows they did in the mid to late 00's.
-People did stop watching because of him. That is fair but is also incomplete. People stopped watching because of Triple H too and basically because the Attitude Era was over and that wrestling product died in 2001 and was never seen again. I think the biggest knock on Cena's run is 08-09 because there was barely any redeeming qualities to what he was involved in. But even still, it wasn't as bad as when he wasn't the main guy anymore and people like Seth Rollins and Kevin Owens got long runs, those were a fukking disaster and also helped boost Cena's case. People began to realize that it wasn't as easy being the n°1 guy.
-He did get booed all the time and it is 100% revisionist to act like for 3-4 years, booing wasn't just "a fun part of being in a WWE show", but there were a ton of fans that legit resented his push. For a period of like 2 years commentary couldn't even acknowledge Cena was booed
I think the first time they felt comfortable doing it was when he beat Edge in Canada in a TLC match.