You're right. It is picking up. I dug a little deeper and found a website that tracks grad transfers. I'm not sure when it was last updated but it reflects just under 150 committed 2018 grad transfers. I'll provide the link at the end of this post.
With respect to evaluating the relative quality of a school's incoming grad transfer class, there's probably a website that does this but I haven't found it yet. I would take exception to your argument, though, that's there no way of assessing who did better. It's arguably easier to size up grad transfer groups than incoming freshmen recruiting classes since grad transfers typically have extensive college game experience under their belt. Another factor that should be part of the equation is the quality of the program the grad transfer came from. For example, in the link below, you'll see that West Virginia's total number of 2018 grad transfers exceeds ours but, unlike IU, West Virginia's guys aren't all from P5 programs.
At first glance, it looks like IU has done very well with respect to 2018 grad transfers relative to other programs.
https://gradtransfertracker.com/2018-committed-transfers/