I use sai for my entire comic making process, and I'll say straight up that if you think it's limited it's because you never learned how to actually draw. The program has amazing brushes, all the tools you could possibly need (except a text tool I'll give you that), and you can create anything from super simple cartoons to hyper realism with it if you just, well, know how to actually draw.
It does have an equivalent of a burn and dodge layer (shade and luminosity) (also I was pretty sure burn and dodge had been confirmed for bad tools because they just don't look good but I guess whatever floats your boat), if you can learn how to draw a simple circle dialogue bubbles aren't a problem, and getting good blending really isn't hard as you can adjust the setting to make any of the brushes a blending tool. (You can even create and add your own brushes if you look up a simple tutorial) It creates some of the smoothest lineart there is, too, so I'm honestly not sure what you guys are going on about with it not being good for lines. Heck it even has one of the best stabilizers I've ever seen.
I will also say that you should buy the legal version. It really is not expensive, and it's a great program that deserves support.