Question about about Tenno and what is inside the Warframes (spoilers)?

Haven't played the second dream, but have always been curious about what Tenno are. Someone explained to me in the game that Tenno are remote controlled empty shells, and there is nothing inside the warframes!?

I thought there would be a humanoid type race of people inside the warframes. I was kinda hoping that one day we would be able to navigate and customize our characters outside the suits of armors. I'm kinda bumped if the explanation is that tenno are just these controlled things from a hive mind. It makes it harder to the character you have spend a long time building and growing I think!

What do you feel Tenno are? I've read online that some things they might just phantasmal energy ("space ghosts") or just forms of matter that can take any shape to fit inside the warframe skeletal structures.