I agree there are a lot of intangibles, particularly on defense, that are hard to quantify with statistics. But, steals and blocks absolutely do begin to tell the story, particularly if they have an extremely high rate in either of them. That doesn't mean you can't be an excellent defender and not get a lot of steals or blocks, but I don't think it's true to say they don't even begin to tell the story.
But, I would say considering OSU is ranked 25th in defensive efficiency according to kenpom, and Forte spends a lot of time on the court, he's leading the league in steals, that he cannot be too much of a liability, given the statistics that are available and that are useful.
Plus, most of the time, Forte draws a relatively weaker offensive player as his defensive assignment. Newberry and Hickey get the better offensive guards/wings.
I think he is getting lumped in with Keiton Page, who absolutely was a defensive liability, and getting painted with the short, white guy brush. Basketball has some very strong stereotypes that are hard to break, in my opinion.
But, besides anecdotal evidence there is no proof Forte is a poor defensive player. I've watched every second of OSU basketball this year in some shape or form, and Forte is consistently a pretty good defender, especially considering his physical limitations. Guys don't just rise and fire over him, like they could with Page and Raymond Penn, because Forte is a much better defender than those two.