I’ve been out of the TaG game for a while now, but I know that SKUSA has been trying to level the playing field, and has changed the weights of those two engines on a couple of occasions. Parity has been an issue with the TaG concept from its inception, and trying to level things with adjusting weight is never the magic bullet. Some engine packages are just stronger at one track than another.
Of course, it sucks for the Rotax and Motori owners, but the Rotax Max Challenge is a great series if you want to stick with that engine. And AFAIK, the RMPKC has the option to run Rotax classes so you can still race with them, just under RMax rules & Mojo tires.