Well Evolve gets some slack because they were attempting to balance a 4v1 game while also attempting to balance perks, monster ability scaling, and the incredible detail that went into everything else in the environment and character designs.
Now, I’m going to list every factor I can think of that would make it harder to release more heroes. Keep in mind that T4 came out one month after Evolve’s release (so in March 2015), and T5 was spread out starting from July 2015, finishing on February 2016. That’s about one new character (including a highly detailed monster) every two months. However, factor in 1-2 new adaptations in the month-long timespan in between. That’s 1-2 new characters every month.
Higher Balancing Difficulty: Evolve
Better Graphical Design: Evolve
More Dynamic Maps: Evolve
More Heroes On Launch: Evolve
Additional Environmental Factors to Balance: Evolve
Much Less Funding: Evolve
GIANT FUCKING MONSTERS: Evolve
More Story In-Game: Evolve
More Collectibles: Overwatch
More Gamemodes: Overwatch
Logically speaking, Overwatch could have, and should have 100% been pumping out more content than Evolve. There is no reason that I can see that they shouldn’t be able to give us more heroes.
P.S: In regards to Campaign and ESL , Evolve kind of but not really had a campaign, and technically Evolve did have an ESL league, but nowhere near the scale of Overwatch’s.