Late to the party - some questions:
Instead of penalizing online teams for doing poorly why not add more incentives to win? At a certain point though you'll have to accept the fact that certain GM's may want to employ a different strategy than you might, and as long as it follows the league rules then acceptance would be the best policy. Making devel even more random than it is in OOTP5 already is a weak design decision, I truly hope that does not occur

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The time when I could see tanking being a most serious issue are when a GM forms an awful team and then quits well before the draft seeds sprout. That is more an issue of poor judgement in allowing that GM in the league in the first place though.