Well, problem is it can end up blocking other owners from using the WW in a reasonable manner. While it's not technically churning, it might be yielding a similar effect. And while other owners can try the same tactic, that would probably just lead to utter chaos and even more frustration in the league.
I think the question should be whether it's an anti-competitive strategy or not, not whether it's churning by definition -- maybe the definition should change to include this.
Also, the answer to that question should probably (again) account for league expectations. Maybe most owners join this league for casual fun and expect to only put in a few minutes a day, if that, while this one owner is putting in tons of time to effectively employ his strategy, which he seems to have thus far. That could be viewed as anti-competitive in itself given some contexts.
IMHO, context does matter a lot, and it's why I have no problems playing in one league that has a fairly restrictive moves limit (40 max) while also another that has no explicit moves limit (but has the usual games/IP limits and is a dynasty-like league). We've also tried a weekly setup w/ the 40-move limit once, but I think some owners felt it was too restrictive and boring -- I just found it to be an interesting challenge that's a bit different than usual. Most of those owners definitely did not like having no moves limits (from our first 2 seasons of play).