The main reason Congress has powers to investigate and bring people in to talk is to make legislation better. There aren't any safeguards to prevent misuse, though, just "custom" - we won't go after them while we're in power, so that they don't go after us while they're in power. Stable as long as the participants can restrain themselves. A fundamental understanding of democracy is that going after political opponents using government powers while you control them is a dumbfuck thing to do and works at cross purposes to the ideal of "peaceful transfer of power".
A committee struck to investigate a couple of things - security shortcomings, and weak points in the certification process - might have been useful. But the former would land mostly on the Speaker's doorstep, and the latter would be too diffuse to attack Republicans, and Trump in particular. The proposed Electoral Count Reform Act which arose through other streams was a good piece of work and had bipartisan support; unfortunately, Democrats didn't seem to want it to get across the line until it could be buried in something else (the recent omnibus appropriations bill). Meanwhile, the J6 Committee set itself up to be a carefully orchestrated made-for-TV production, and proceeded along those lines.