The problem with SMN is that adding more summons would simply results in the same gameplay.
If SMN would cycle on 90s rather than 60s, maybe it could help to free space for job creativity.

Lorewise wouldn't it feel pretty weird to summon Shiva as she's a person before being a primal?
What if SMN had 90s ability that could empower and extend a specific summon, for example summons Eden Titan instead of regular Titan?
And yes it would come with the kart.

In my opinion, SMN would benefit greatly by separating itself from the 120s meta.
But that's another topic.