If your work consists entirely of reading and writing documents, and it sounds like portability is very important, you might actually be fine with the iPad. But if you think you ever might want a real web browser or something like that, you might want the Mac. And even though you're using the iPad with keyboard, the Mac keyboard is *far* better.
For me the answer is Mac 100% always. iPad is way too limited and is basically just a TV and book reader for me at this point. That may not be true for you.
I don't think the MacBook Pro is any less portable than an iPad Pro with keyboard. I have both and the MBP is actually more portable in my opinion. Feels a lot more sturdy when closed up. Unless you really want to be able to take that keyboard off, the extra weight is worth it. And don't forget about the trackpad.