I know the Century Hyatt is not even in the same league, but I stayed there a few weeks ago and had very good Diamond recognition. I guess I've read here that the average Park rooms are 50-100% bigger than the average Century rooms; we were given a room at the Century which was easily 50% bigger than the standard Century room, so in terms of room size, we probably ended up with as many square meters as we would have at the Park.

And paid about 1/3-1/2 of the Yen per night.

Just FYI. I posted a trip report, if oy search for "shinjuku" last 30 days, you'll find it (sorry for my lame technical skills in linking).