Other than being a good time to go grab a coffee, I feel infected compound attacks don't add much to the game. They are not interesting or challenging, even with 4-5 survivors back. Only in the rare instance that one left 1-2 players behind are these attacks relevant.
They were at lower levels. And I'm sure there are players that find them enjoyable/challenging at other levels.
But it appears that infected attack severity (spawn number, rare zombie fraction, etc) is tied only to player level, not a player's previous success rate with infected attacks. Seems like compound attacks could be made interesting again adding one or two more variables.