I agree in principle. However, 20% is too high. Players invest time and/or money to get to their current level, so such a massive drop would discourage the real players from playing. Keep in mind, tankers only reside in the upper levels of the associations, and there are probably only several hundred (or at most, a couple of thousand) of them. So the punishment should not negatively affect many more genuine players.

That aside, I particularly hate tankers who manipulate league results. Yesterday, my 115% team was beaten by a 144% tanker, who had earlier contrived to lose against my opponents. As a result, I dropped to second in my league. Today, I'm playing against another 137% tanker.