Let me spell it out. Disagreeing with the Talmud's opinion about Bar Kochva is not "denying oral law." First of all, there were many sages who were involved in the hundreds of years of redaction process behind the finished product of Talmud, and there was not one single opinion on most things. Certainly at the time of the revolt itself, the rabbis were not against it. Certainly, after the results, in dealing with the aftermath and destruction of Jewish life on a scale (by percentage) greater even than the holocaust, the rabbis had reason to be against it. Manch calls that a "bias" - maybe that's not the friendliest term to use, but it's probably accurate. Of course there was a bias to not have another revolt which would result in a million murdered Jews and especially at a time when Jews were incapable of victory and would be slaughtered. So the Talmud redactors had good reason to downplay the revolt. So too, the sages in the generations of bar kochva and shortly after him, had reason to point out his flaws given how it turned into a disaster where so many loved ones were lost and innocent men women and children destroyed. Are you going to react to that positively? No one in their right mind would.
Secondly, what that site is referring to is disputing the interpretations of Jewish law similar to the way the Baltusians and Tzaddokim did (aka Sadducees). An example would be claiming that tefillin don't go on the head - something all the sages agreed on was an oral law from sinai. Or if somebody came along and tried to say the beautiful fruit is not an esrog. Something along those lines. That person would be an apikorus. Not a person who differs in opinion about a Jewish historical figure! (even if they are mistaken). That simply does not fit the bill of "denying the Oral Law." Jews are allowed to have opinions about things. And even sometimes personally disagree with rabbis, yes, *gasp!
You need to be careful about slinging insults around.