Boss thinks the CMS that another dev built over the course of a good year, will make customers say "ooooh yeah, I will definately come to you and pay a shitload of money for a buggy and unfinished system, even tho I will never be able to leave with a working copy of my website like I could with wordpress".

The whole effing things is based on an old, outdated version of a popular PHP framework.

Oh yeah, and I can not update <the framework> because the dev has tinkered with the core files :)
Yay.

The whole fucking thing won't run on PHP7 and will explode right into my boss's face.

Not mine though, because I will be gone by then :)