I think his initial tweet is phrased very retardedly (ZUN's "grip" on the series? it's HIS series and he lets people do whatever they want with fan works) but his overall sentiment is more understandable, most seem to agree the last few Touhou games he's made are pretty unremarkable, but on the other hand...it's a solo dev hobby project sold pretty cheap (and pirated by most) so can you really hold it against ZUN if his best years are behind him?