[chickin]

Firstly, congrats on having a popular project, caring about contributors, and seeking advice on how to handle this tricky situation.

When giving pushback, try to avoid raising the stakes, i.e. avoid public criticism, don't issue ultimatums.

If you have a private chat, that'd be great.

If not, try to state your concerns as plainly and non-judgementally as possible, from the perspective of your project.

"Hey X, I'm glad that you are and have been contributing so much to the project. There's a few different ways I see the program and codebase evolving, and I'm keen to work together on figuring out that right path.

It looks like there are places that have different visions, and if you could split PRs into smaller PRs, we can more easily find the changes that fit both our visions."

If there truly is disagreement on some PRs, you can be polite but firm, "I can see the value in X because Y, but this compromises Z, which is a core value of the project."

You have merge access, and should also consider whether this contributor is worth the hassle of all of what I just said. (In which case, skip straight to "polite but firm").