Oni has his Patreon set up to charge his patrons every month. I would argue that if he is asking for monthly payments he should be providing monthly content. I think he's been getting better at that over the last few months but as you say, he usually releases major updates every 3 months or so. Updates between that time, if there are any, are usually minor bugfixes.
He's getting paid upwards of $40,000 to $45,000 per year to basically string the game along as long as possible. He's already openly stated that this is only a hobby for him and he has no plans on ever focusing on the game full-time. Take one look at his version designations and you can immediately tell that he has no goal of ever releasing a "1.0" version, because once his version number gets up to 0.999 he will just add another decimal onto the end so he can continue stringing the project along.
He's not interested in bringing in outside help for art anymore (even the work he has commissioned in the past went unused), and he's not interested in bringing in outside programmers to streamline the code.
I have nothing against people getting paid for their hobbies, but when you're making a LOT of money from your supporters and you're providing very little to show for it, it's entirely justified that those people financially supporting his hobby might feel slighted or taken advantage of.
Awhile back when I first found Rogue-Like, I was a Patreon supporter of Oni's. I have long since cancelled my support for the reasons outlined above and I feel no sympathy for Oni, nor will I defend him. People can give their money away if they want, but I for one am not going to throw money at a guy who's willfully stringing us along with half-empty promises of future content. I love his art. I hate his business tactics.
Just my opinions.