So I'm sure there are some who may also be able to answer your great questions, but I'll take a stab at them.
It was no secret that DL and KL hated the Leonard Bowl. They are both fiercely competitive, but very family oriented men. They had to make agreements on Leonard Bowl week to not talk about football. They often wouldn't even speak that week so the topic didn't come up.
Rochester did not lose many athletes to SHG. There were a few that lived in the RSD that went there, but most stayed. Both are good schools so there really wasn't an educational motivation to flee Rochester. Almost all of the kids who play at Rochester grew up there. Despite the claims, Rochester and DL do not go out and poach athletes from other schools. Do some come for the program? Absolutely...but the number of impactful players who didn't grow up playing Rocket JFL is less than 10 over the last 14 years.
By the same token, most of SHG's players rose up thru Catholic schools. Yes, they have been a recipient of lots of public school talent, but good on them and good on the kids for taking advantage of getting a better education than Springfield Public Schools can provide.
There are no other Catholic HSs in Springfield and the other private schools don't have good football programs. The closest decent Catholic programs are way outside a 30 mile radius (QND, BCC, St. T).
I've seen and talked to KL at SHG games so yes he still goes, but he's also been climbing the Rocket stands to be an eye in the sky for every Rocket playoff game. Remember all three of his grandsons are playing Rocket football (Freshman, 7th grade, 3rd grade).
By-and-large, the Rocket and SHG fan bases are on friendly terms. DL and KL were heavily involved in FCA as are many of their athletes. They both know (knew) the kids on the other team on a first name basis.
Also, to clear up one more misconception about Springfield kids going to Rochester....yes there are kids with a Springfield postal address who live in the RSD. Some posters apparently believe the Rochester National Guard conquered Springfield territory because they don't know how school districts work. The RSD boundaries have existed since the early 1900s and Springfield city proper expanded into the RSD...mainly because people wanted to flee Springfield for better schools. Not quite sure what the motivation is for posters pointing out Springfield addresses at RSD. No one has been able to tell me how a postal address confers a special advantage for football. Those same posters would be shocked to know there are kids with Rochester addresses attending Glenwood schools (see New City area).
Again...thanks for the honest questions!