As with most merc strats, you never want them to be too spamable, I think the devs want to test this out since we are talking about an unit with 40 range resist and imp stats right out of the gate.
I think their viability is up for debate right now, as people will still need to figure out how many is optimal due to all the overkill.
Late game, I think the comp is going to be something like 1 jeager for every 5 caroleans which allows for enough anti infantry/goon fire while caroleans keep hand cav away.
I think caroleans are fine as they are. maybe too spammable but their stats and roles have clear weaknesses