If you're trying to learn Common Lisp, then no 'cl' is not sufficient. It ads a few CL features to Emacs lisp, but it isn't the same thing at all.

If you're just trying to write Emacs extensions, then it's a nice extension to the language which makes it slightly more tolerable.

I've used the CL package in Emacs (with the proviso that if you're using it to build an Emacs library, as I was, then you're supposed to restrict its use to compile time, which is weird and takes back most of the value). It doesn't make Emacs Lisp into anything much like Common Lisp. The two are very different languages. The CL extensions in Emacs are kind of useful if you already know CL, but they're also a strap-on and the result is predictably a monstrosity.

I think you'd be better off picking which of the two languages you're interested in and learning that.

Thanks, it's clear now. I was confused about the purpose of the cl package. Just checked the manual again and it is not misleading.

I think it was my wishful thinking as I was looking for something more concise than elisp's set functions.