The other issue is there are massive problems with acting like the Guilds are neutral factions.
Take the Cult of Rakdos for example. As I mentioned they're a sadomasochistic circus-themed death cult centered on a demon lord (named Rakdos) that control most of Ravnica's entertainment industry. And the mining industry for some reason.
A notable member of the Cult of Rakdos is Massacre Girl, a serial killer who takes assassination contracts on the understanding that there WILL be lots of collateral murders.
I know some people don't like Alignment, but the Cult of Rakdos is Chaotic Evil. Even if there are members who don't partake in torturing and murdering people they're still supporting the members who do.
And The Guildmaster's Guide to Ravnica presents them as being a valid option for PCs to join.
Or there's the Orzhov Syndicate. They're like if the Mafia and Catholic Church back during the time of the Inquisitions combined and founded a bank.
If you die owing them money they enslave your soul until your debt is paid off. And your debt only decreases if they put your soul to work and the debt keeps increasing otherwise.
They're obsessed with bloodlines and their founding families were the only ones allowed to hold the upper levels of power until right before the War of the Spark. And because they can become ghosts who still own property there's the ultimate glass ceiling.
The Orzhov run a fake religion where they purge independant thoughts, preach a prosperity gospel, and use the flesh of sacrifices to create abominations known as Thrulls. They torture debtors (whipping, pillories, removal of limbs, etc.) and there's a specific monster who debtors can feed themselves to to try to pay off some of their debts.
And The Guildmaster's Guide to Ravnica presents them as being a valid option for PCs to join. It outright says that high-ranking Orzhov PCs will be able to have the Guild's enslaved souls do stuff for them as if there's nothing objectionable about it. The only negative thing it says is that the Orzhov won't like a PC using the enslaved souls for too long because it'll decrease their debts.
The book basically says 'Don't overwork your debt slaves because they might get closer to freedom.'
I'm all for letting PCs be villains in Evil campaigns, but the book doesn't present it that way.