Solano, while a useful unit, is not popular on DMM at the moment for practicality reasons. Specifically, her downtime. Even the black summoner suffers.

As for the DPS comparison, you completely ignored attack speed. In the amount of time it takes for a mage to attack, Nadia will have hit almost three times. If three mages are hitting for 1k each and Nadia is hitting for 2k each, you can see how the math turns out. This is of course different if you have a caster with an attack buff(Patra/Mole) but even then it's a case of limited uptime versus permanent uptime. This is also not accounting for mage range, the superb defensive stats of Nadia and space considerations(it's easier to have space for one unit versus three) but I digress.

Also, you continue to ignore the fact that someone else needs to do Gellius's DPS for him, since he contributes jack squat. As much of a wall as he is, he is very much a non-entity by himself - he needs someone to tank for. If left unattended, even purple goblins will escape. By comparison, it doesn't matter how many purple/red/black goblins there are, Nadia will stop every single one every time once active.

Nadia's offense is again situational , depending on the enemies resistances.
The only thing she can't penetrate is high-tier golems. Mages happen to suck against those too. I guess Solano doesn't, but Rikka is better.



edit: ...lol exk.