I don't want to minimize the 2:12, especially for a first marathon effort. But, it's 7-10 minutes off the world leaders' pace, at the best woman's pace, and guys from the US have been doing this for decades. My inclination is to consider that maybe our pro's are not cutting it.
Just using myself as an anecdotal data point, back in the day I was a middling collegiate runner... kind of a normal #4-7 on an average program kind of guy. I felt like I worked hard, though. On a whim, I ran a marathon while in school. I completely fell apart on the last 5 miles and finished in 2:36. After school, I ran with a good group that had a handful of OT qualifiers. I was taking it seriously compared to some (as most stopped running completely after school), but I had a new job, was newly married, just had a child, etc etc. Compared to collegiate running, I was a serious hobby jogger and ran in the mid-2:20s. You could never convince me that a lot of the good collegiate guys couldn't run way faster (and under 2:12).
If you just took a bunch of the good collegiates and said, "Ok, I know you thought we were racing 8K this weekend, but surprise, we're running a marathon instead!" Then, no, there would not be many sub 2:12s. On the other hand, if you took all the upper-tier distance teams (say, top 20), and at the end of track season it was determined that the XC national meet would be a marathon rather than the 10K at Panarama Farms, and if they "buy in" was the same as it is for Nationals. Then, assuming they could all have a first marathon experience in June (to sh*t the bed and learn the event a little), I think A LOT would be break 2:12 in November.
I am not saying this to be mean, but our pros are currently more valued as marketing agents rather than fast runners. The two are related, but not exactly the same, especially when it comes to roads and trails as opposed to the track. If a relative unknown 13:30 guy comes out of school, doesn't do social media, doesn't really do interviews, but puts his down and trains and runs 2:09 at Boston (lets say, a US #5-#7 guy), he will probably not fare well (financially speaking) compared to the DeanK, AllieO, SethDeMore types. Ideally, one could do both, which is what I think Mantz is trying to do, but it's two different skillsets, and frankly, the people drawn to either camp may not really appreciate a person who cold do both. So, the marketers are winning.
ALL this said, and I know I am being longwinded here, but there does seem to be a resurgence in running well in XC and track in high school and college, and to me, that's a very good thing. The extent of the marathon's popularity over 5Ks, 10Ks, and just general fitness is messed up. Lets mostly leave the marathon to the overweight 50 year olds (all the best to them!), and lets have more athletes do the 5K, 10K, summer track meets, etc.