I think it good on them to go after artists those who haven't produced any work for 3-4 months, it would keep the leeches in check & would provide better experience.
1) Even if I agreed with you, that wouldn't apply here. There's a massive difference between being a leech and taking time to do a big project.
Your impatience doesn't make him a leech.
2) I don't think it's worth going after inactive devs at the cost of punishing devs like this who are putting in a consistent effort to put out quality work.
If you don't like his upload rate, that's fine. Just don't pay him on patreon. Let people who want to support him, do so.
3) Understand that just because he doesn't upload every month doesn't mean he's lazy. Teasers are a great way to show supporters that he's working while drumming up hype and getting more support. It honestly should be standard for most devs given that it lets people see progress in action.
If you want quality animations, renders, and writing from one man, then it's gonna take time. Lot's of time.
The only you can get something faster is to sacrifice one of those. The teasers are a great compromise.