The way I see it you can never have too many different tools in your arsenal. After a while you get to a point where you can easily CC and level anything new coming in on Nutaku. This might change if we get a steadier stream of events.

I have found on DMM (also free on there) I am spoiled for choice and can pick and choose a lot more thanks mainly to revivals. Plus there never seems to be a shortage of silver fodder thanks to guaranteed first run drops. Unit-wise my account there is a lot stronger even though I've been playing it about 5 months compared to 9 on Nutaku. Extra units, extra SCs, constant events means a different game in many respects.

All the breaks on Nutaku really hindered my progress where on DMM its a case of what do I focus on building now, put off until later and outright ignore because I can't do it all. For free players on Nutaku it can often be a case of using whatever you can get and being versatile to plug weaknesses in your lineup.