Yes, I would advocate the removal of the SSO-less trial discount. Rationale: most of these "trials" are otherwise fully capable and lend themselves very well to becoming long-term ways of doing things. "Nothing is more definitive than the temporary."

Or, to view it from a different angle - SSO is not a/the feature that should be removed to make it the "trial".

And from yet another angle: you could consider removing (or not offering) SSO similar to selling a car without seat belts (ignoring aspects of legality). It's not a problem until it is. But if you want the seat belts to be effective, you need to always have and use them from minute zero.