Forcing a gank is when you go for a gank that will almost certainly fail. Never force a gank, it will only put you and/or your lane behind. (here's a tip: don't gank lanes that are behind already, help the lane that is ahead get far enough ahead that they can keep solo killing their lane opponent. After they can do that, then help the other lane, that way you are guaranteed at least one lane that is ahead, instead of maybe no lanes. Once the one lane is ahead, they can usually begin to roam with you as well, for stronger 3 man ganks.) Doing a tower dive is not the same as a forced gank though, and when done right can be utterly demoralizing for the enemy to know they aren't even safe under tower anymore. The part of Lee that falls off late is his damage, and that is when you don't build damage. Late game his role as a damage dealer is changed into a utility front liner (unless you built damage, then you are more of an assassin), so he doesn't fall off in the way you think. Also, you shouldn't have to gank past mid game, that is when everyone should be grouping up anyway.