Old Creative Suite era versions of Adobe Illustrator have serious limitations compared to the current Creative Cloud version. It has been nearly 12 years since the last CS version (CS6) was released. Quite a few features have been added to Illustrator since then.
Much of the corporate world has its branding assets developed using Adobe Illustrator. Most of these logos tend to be "flat" in their design (flat colors, no effects or embellishments). That kind of artwork can usually be imported into non-native graphics apps (CorelDRAW, Affinity Designer, etc) accurately. But when they start baking certain kinds of gradients, transparency effects, transparency blending modes or other kinds of Illustrator-centric effects into the artwork it creates big problems for non-native apps. It really requires a current version of Illustrator to open those kinds of art files successfully.
Anyone who doesn't need to handle customer provided artwork, particularly artwork from big companies, can get by without Adobe Illustrator. They can use whatever software they want. I rely on Adobe Illustrator frequently for accurately opening corporate artwork and I often use Astute Graphics' Vector First Aid plugin for Illustrator to automatically fix problems in assets harvested out of PDF files. Technically PDF is not supposed to be used for further editing of artwork. But often that's the "best" thing we can get from a client. It's better than some dopey pixel-based image in PNG or JPEG format.
Aside from that issue there are certain things I really like in Illustrator that aren't found in rival apps. The current version has some pretty useful features that won't be in any old "CS" version.
