Mag is (...) out of the meta

There's no "meta".

There's a meta if you're doing specific bosses like eidolons, profit-taker and so on, or if you're doing crazy runs like doing hours of survival. But for normal gameplay (sorties/arbitrations) Mag is as perfectly usable as most other frames, provided you have the resources to make a good build.

Mag does great at high level with her 2, mostly. But you can make builds to lockdown maps with 1, or stall guns with the 3 and its augment. The only downside is that you need a constant supply of energy to spam your abilities, so things like a high-efficiency build, constant zenurik dash, and/or arcane energize help a lot.

Also, arcane guardian + adaptation + her 4 do wonders for survivability.