Absolutely and VERY STRONGLY suggest we have status indicators on the card itself. Won’t clutter at all, but will make life way easier.
New members to the project don’t have a clue whether a card has a sub-task or not, and how many left to be completed, till they open it. I don’t see any reason, whatsoever, why not.
A short indicator e.g. 2/5
^indicating 2 out of 5 tasks are done. Helping everyone know it without opening each separate card.