from my experience with accelerators and company builders a concept that makes sense is already enough. Makes sense includes of course feedback from potential customers, competitor analysis and so on.
A prototype makes it better though as people can directly get the idea using it.
An MVP can be significant additional time where these partners see their competence helping you getting there.
Specially in Gaming - working in casual gaming for more than 6 years now - an MVP can get costly and evaluating an MVP as well.
So I would take your prototype and talk to them. Worst thing happening is, they say you have to come back with an MVP.
Do the normal accelerators actually support gaming projects? I always believed this is too fa away from their core business understanding.
And Gaming is quite complex and the market entry barriers are quite high meanwhile
If you want feedback on your prototype or some other info feel free to contact me. I'm based outside US too ;)