Tl;dr apologies
The rankings can be completely wrong from time to time, for sure. For a lot of really talented kids, if the big state schools don't notice or don't offer them, then other P5 teams often don't either. Kids can also receive too high of rankings for having great size right away, happens on the OL all the damn time. A kid will be ~290+ and steamrolling other high schoolers but they may have already reached their peak athletically or framewise. Meanwhile, a 6'7" kid with incredible athleticism and a frame that can hold 315lbs will be a 2* because they are only 245lbs (as juniors often times) and the big boy programs don't want to invest multiple years waiting for them to be ready. It's how some G5 teams can hang with bigger programs, their OL have all been in the pipeline for years and are nasty.
Two of your commits perfectly encapsulate what I would look for to call underrated.
TE Austin Allen. TEs can be so hard to judge on film, you can get some idea of their blocking but highlights are never going to show all the drops (obviously!). So with a lower rated 3* like Allen, what I want to see is teams in the area offering him, as they likely have seen him in person more as well as working him out in camps and stuff. He's also skinny, which doesn't matter as I'm sure your coaches have seen him finishing plays and playing mean despite his lack of weight.
LB Willie Hampton. Similar to what I was saying about Allen, short of having a ton of P5 offers the next best thing is seeing two different staffs in the area (UCF and FAU) come to the conclusion that he's worth an offer. Yeah, Miami, FSU, and Florida didn't offer him, just one of those offers and the kid blows up and every ACC and likely some SEC teams go after him. But they also can't possibly offer all of the underrated talent in Florida, now you guys have a speedy LB with good size to come play in the B1G. This is the type of kid who helps beat the Iowas/Wisconsins/Michigan States. Who cares if he's not a 4*.
Ultimately, it's true that you need to recruit well to win. But it's important that the staff sees guys they like in person and that they land them because it only hurts missing out on the 5*s if you don't have other options in place. Relax and trust the staff to finish out the class strong.
