Depends on what you consider a "problem", I think. I think there's a problem, not because I think they are particularly hard to beat, but mostly because they take a long time to die due to relatively high HP, and because they are absolutely everywhere in Arena/Arena Assault these days. The same applies to armour teams too, for me. To the point that both have just become really boring to deal with, and there are weeks where I just don't bother with Arena Assault because I don't feel like grinding down seven armour or dragon teams in a row.
I think it's mostly a matchmaking problem - just let the dragon and armour teams get matched against other dragon or armour teams, and let people like me who want to use more varied teams play against other such players, and I think there'd be less complaints. I'm sure it's easier said than done, but the current arena matchmaking system is really awful, and I think something needs to be done with it.