I am a fellow Ibis Paint X user and it is one of the app weakness that it eats RAM like Chrome does, and tends to be laggy.
I have observed some people indeed draw their comic in Ibis, and you are able to do so thanks to its features. Although I don't think it is the ideal app for it due to the limitations of features and performance, especially compared to desktop applications like Photoshop or CSP. I do not make comic so I am not really knowledgeable.
What I always do when there are too many ads is to disable mobile data. I don't know if that works, though; some applications have way to cheat it by giving you "wait" screen and I have not touched Medibang in years. Or you can cross-use Ibis and Medibang (e.g. sketching with Ibis but lining with Medibang), but I can see how it can be a hassle.