I can't and would not write more than two chapters in a week.
Speaking honestly, you CAN, but you have to want to, and it takes practice and discipline, as well as proper planning. Writing is a skill that develops with effort. The harder you push yourself, the more you will progress.
Now, it sounds like you are also including editing and re-writing as part of this process as well. Personally, I recommend keeping the writing and revising processes entirely separate, and only revise once you're completely finished with a work. Not only does this save you from a lot of unneeded edits, but switching between writing and editing over and over as you work on a chapter actually severely hampers your ability to produce work quickly. Its better to write out an entire draft, then do all revisions, rather than tweak as you go.
Short Chapters
Chapter length on here is not the same as chapter length in a real book. Having written in multiple formats, I personally find it much more efficient to break large chapters into 600-800 word chunks for chapters on here because that generates more exposure. There is nothing wrong with shorter chapters, so long as the frequency is high.
Now, you said you can only do 1-2 chapters a week. Are these chapters 700 words long? Because if so, that's 1400 words a week. That is, and I mean absolutely no offense by this, not a good writing speed. You should easily be able to hit 3500 words a week, if you write every day. If you don't mind me asking, what is your typical writing procedure? I might be able to help you find out how to improve your output.
I like to use simple and common words
Having a simple style is fine. Plenty of successful authors have done well with simple writing. Denigrating authors who use more complex language, however, is not cool.
Classic literature books are novels. Modern novels are novels. Web serials are novels. There is no difference, aside from personal taste. Hell, the classic literature of today was sometimes considered the simple, light writing of yesterday.
My grammar is not perfect.
No one is expecting it to be. However, it is expected of a writer that they are perpetually trying to improve their grasp on it, especially if English is not their first language.