As far as Marvel films go, they will take a steep decline going into Phase 4. Considering how superhero films that only focused on promoting specific agendas rather than caring about their story such as Captain Marvel and X-Men: Dark Phoenix performed poorly when it came to public critical reception, things don't look bright for Marvel's future going forward with the reveal of such things as having a female bisexual Thor for no real reason when the original Thor's still around or making a film on such an obscure character as Shang Chi just to appeal to the Asian demographics, despite him having no other engaging qualities and Master Wong always having the option for a solo movie if wanting to appeal to Asians. Leaving aside the political agendas, there's also no real plan for Phase 4 going forward. Even though not everything about the MCU was planned in advance, each movie held at least some level of building to something grander. After Endgame, however, that's almost non-existent with what build up that is there in post-Endgame films such as Far From Home being a major step down in scale.
As for DC, they'll have its own problem of having become Marvel-Lite with the DCEU. They failed at being the gritty equivalent with Man of Steel and Batman V Superman, Wonder Woman was just an OK action flick, Aquaman is the type of film that can only be enjoyed by turning your brain off and embracing the ridiculousness of it and Shazam, whilst a fun action-comedy with some good ideas, had some problems in its plot and was at best the poor man's version of the first film of Raimi's Spider-Man trilogy. The change in tone after BVS seems to have been a positive move for DC financially, though it won't take long for superhero fatigue to set in fast when doing nothing to surpass Marvel. Their animated films are better, though even the best of their new animated continuity doesn't tend to be much more than middle of the road films.
The best case scenario is that the superhero fatigue people are experiencing will lead to more deconstructions of superhero stories in the style of Watchmen. Logan has proven how gritty takes of the genre can work both critically and financially, as has The Boys if including TV Series. Captain America: Civil War was also a step in this direction and the success of films such as The Dark Knight and Captain America: The Winter Soldier have proven how superhero stories can easily slot into other genres such as crime thrillers rather than being a specific genre. Unfortunately, the chances of seeing many of these now that Disney has completely assimilated many of the Sony copyrights into their far more family-friendly brand or the DCEU being persuaded not to go for gritty stories after BVS make the chances of seeing another Watchmen-esque deconstruction or even just another Kick Ass seem slim as far as the film medium goes.