With 21/35 you get two choices:
1) Treat it like air. That means you get 5 minutes of MDL time at 130'. Then you have to pay back every minute you owe. So, for a 20 minute dive, you get 22 minutes of deco on 21/35.
2) Use the 21/35 setpoint. You go 1:1 at 150' and get 5 minutes of credit for every 10' shallower, but this is predicated on using 50% (otherwise your deco doubles). So, for a 20 minute dive you get 20 minutes of deco on 21/35.
You lose the O2 window. You only have the gradient to deco...so you're doing a Buhlmann w/Gradient Factors deco schedule...bleh.
A 130' dive on 21/35 is much better done with O2 deco than 32% or even 50%. ~11 minutes of deco for a 20 minute dive.
I don't think anybody is disputing that.