Pay-to-play has more scripts so people can switch scripts and there is a lot more places to bot.
In free-to-play, it's a lot smaller and less scripts to run. So, I imagine free-to-play just makes it easier to catch bots but I doubt there's a difference between the bot detection system they have. All probably same.
I don't actually know. Just my guess on it.
I hope that makes a little sense, sorry if it didn't.