weisswurst I personally value Glicko ladder position much more than the league win because Glicko reflects your long term results while one win in tournament could mean that you simply had just luck. Although you do not need to be necesarily the best to win GM, we have to say that to get to GM and win it requires a lot of skill of course and you can bet that the players in GM are from the best.
Regarding the fair play, as a member of player commitee, I can tell you that things like declaring a war and disbanding units afterwards are considered unsportsmanlike and if reported will result in a penalty for the player who did so (warning, deduction of points or ban). On the other hand playing impacts of any kind is always ok at least in my opinion. The commitee has 5 members and we vote in such situations and the commitee members may have different opinions on different situations so in general the line is somewhere between the impacts and disbanding units in war but nobody can give you a definite answer until you raise a specific case.
Like pajada said, just try to play fair and enjoy the game.
