He is, though. It's just that this particular cult has been around for so long that it's "traditional", kinda like tobacco and alcohol were not counted as "narcotics" in most jurisdictions.
I would be completely fine with saying that there do exist cults operating within the Catholic Church. Arguably, monasteries, especially the more isolated ones, are very much cults, with the cloistered lifestyle, complete dedication to the faith, strict authority, and requirement to cut previous ties to join, plus cutting ties if deciding to leave. I'd even agree that the priesthood constitutes somewhat of a cult, for similar reasons.
However, claiming that all of the hundreds of millions of lay Catholic believers are members of a cult is ludicrous.
Or how about Mormons? Are they a cult or not? If not, were they a cult at some point, and when exactly did they stop being one?
If he were a cult leader, you would see him abusing this power constantly to reassert his power. Instead, papal bulls are rare, we'll thought out, and generally limited to nuances of the faith, not some capricious overhauls.
That's not to say that popes, even the most admired ones in recent times, have not engaged in horrid behaviors that are a detriment to humanity, and also in outright corruption. They've hidden the extent of pedophilia in the priesthood, they preach and run campaigns against condom use in some of the areas worse affected by STDs in the world, they systematically exclude women and LGBT people from the church leadership, and many others. I am not some lover of the pope, and I am an atheist myself.
About mormonism I honestly know too little to have a good opinion. It certainly seems to have started as a cult, but no idea if it still is, and even less so when it might have stopped being one.