There is absolutely zero evidence that MDMA antagonizes anything LSD does that would effectively be anti-psychotic.
While MDMA does give a positive feeling, the combination can still be quite crazy trust me. Helping to avoid a terrorizing trip... hmmh dread may act as the final drop to push a person over the edge, but a much more pertinent issue is losing sight of real vs. mind-manifested.
If a person is at least somewhat resilient in this sense of reality and not predisposed to psychosis, LSD won't really cause a psychosis by itself, worst it probably does at that point is a temporary drug-induced psychotic episode or a delusional episode that passes when the drug wears off.
A positive mindstate helping to avoid dreadful trips doesn't weigh up against the tendency of such drugs to undermine your sense of reality.
Drugs like LSD mostly suppress the thalamus which is a relay station that normally governs higher levels of consciousness and without that government the brain is left more 'free' to do its thing (which can be risky if you are a person who has a brain that can't handle that freedom and go psychotic, and start mistaking signals). MDMA suppresses the limbic system which is the center of learned emotional reflexes, which helps dissolve fears and pre-programmed feelings we associate with things.
But basically it is another way to disinhibit systems. From this I would NOT expect a reduced risk of too weakened boundaries.
MDMA does not help guard the boundaries and differentiation of real vs. fantasy/thought or abnormal thoughts and behavior.
Combining these two is worse than either alone in risking psychosis, even if it is only my word against those two people you asked... general drug interactions tell us that if nothing else a drug combination is a complication.
Honestly you are playing with fire to begin with, taking psychedelics when predisposed and diagnosed. Sure they are (generally) beautiful, but I don't think they are worth risking your mental health over like that. Take care of yourself.