There is an extremely unnecessary delay after firing S4 hero special skills when it generates an Underwild gem. During that delay period, you are unable to activate your other heroes’ special skills.
For all other heroes, you are able to immediately consecutively fire their special skills back to back (regardless of animation time). It would make sense to make S4 heroes congruent to all other heroes in this aspect.
While this may seem like a small issue, it is particularly inconvenient during titan battles and on event stages where time is a factor. It disrupts the flow of battle and can lead to not firing a hero’s special skill when you thought you clicked on the hero due to it being during that Underwild gem spawn delay time frame. @Petri
If I were to think a reason of that delay, it helps people not to make a move on the board immediately after activating the hero special, that may combine the underwild gem that is spawning.
But on the other hand, as you said, it disrupts the flow when you try to consecutively fire the heroes specials.
What I usually do is put the S4 hero on the most right position so I can fire the specials back to back from left to right. It might not be the best solution but it guarantees firing all the specials without disruption.