I think the best way is to alert everyone of a migration to a different panel at the same pricing/lower pricing, and give alternative to those who don't wish to migrate to remain with cPanel at an additional extra.
Make sure all your plugins are good ones and well developed.
I have currently 15 plugins in a wordpress page and the website loads super fast (shared hosting). While in another website i had only 5 and it was super slow.(some random's plugin fault).