Biden did not pardon any of the 1/6 mob! Trump did as soon as he took office. Biden pardoned the 1/6 committee because of the felons threat to go after everyone on the committee and witnesses. Garland was a big mistake, but at least he followed the law.
"de facto" means "in effect", or "in all but name". Biden appointed Garland because it was clear that Garland would never hang so much as a parking ticket on any of the Jan 6 ringleaders. That was Garland's job. This was a political decision tailored to *prevent* accountability.
And so it came to pass.
And of course none of that was "following the law", it was the biggest dereliction of duty in human history. Obstruction of justice. Same as leaving Wray in office despite his flagrant inaction in the run-up to Jan 6 when everybody and their puppy dog saw it coming weeks out.