It sure smells like throw-away ticketing to me. "Illegal" is too strong a word - this certainly isn't illegal anywhere I'm aware of. But it quite possibly violates the airline's CoC, which means they could, in theory, try to make life uncomfortable for you in one way or another, assuming you're doing all of this on one airline.

Whether 6 times is enough, I don't know. Personally, I'd find a way to leverage two airlines and perhaps some sort of open-ended ticket type, if one exists. 6 throw-away tickets would exceed my personal risk tolerance on any airline where I cared about my miles and elite status. Which, if I were flying long-haul international J/F (which this appears to be), would be all of them.