True - I let my 2.4 29er tyres down to 15 once and it was like riding in jelly - it’s like someone saying 80psi in road tyres is acceptable; until you have to get out of the saddle or put any power down and it feels like you’ve got a flat tyre. Or put on 20kgs.
My 2.35 29er tyres feel too squishy at below 20psi, I can't believe that this is at all rideable.