Cevolink went some way to balancing the infected / survivors, but Insanity Versus was much more fun (and challenging)
2 Tanks spawning in quick succession on the finales, 4 tanks when the rescue vehicle arrived, boomers able to walk and vomit - much more of a challenge for a good, well organised survivor team. This went along way to fixing the "average survivors" team making all the way to the end even though they were put through the mill at every opportunity by the infected. Now the same team wouldn't stand a chance!
I think as a result we all became better survivor players