Sam and oyoyoy, yes, you get the mitzvah of Talmud Torah just by saying words of Torah shebichsav, mah she’ein kein TSB”P. I think that it does come out the opposite for a siyum, which, I see R’ Moshe holds, requires havana.
Without a legitimate pirush, there’s no legitimate havana in TSB”C. Try learning the parsha of tefillin or ayin tachas ayin without TSB”P. We need to learn it with a solid mesorah based pirush
In other words, Torah shebichsav needs Torah sheba’al peh. Gemara is already Torah sheba’al peh, and doesn’t inherently need a pirush.