Combos were already a pretty niche mechanic, but now that they can't be upgraded the timing window is fixed at 3 seconds and the max gain is only 6 coins for a x5 combo ! Compared to a 4 second window and 15 coins at x5 combo or even 18 or 20 coins with Dr. Hoot ! (I don't remember if it was 18 or 20 but either way that's a lot more !!)
Combos really could be a great mechanic of the game if it was buffed, like if there was a new worker centered around them or something (because now workers only have one ability and Dr.Hoot is already the patience worker)