This is an extreme example of a general concept: diminishing rates of return. The first +action in your deck (say Necropolis) can be extremely valuable (e.g. Ghost Ship/Torturer), the next is less (sure Xroads/Gship/Tort x2 takes them to zero cards if they won't take curses), but additional +actions have much smaller gaps between them (e.g. Nec/Xroads/Gship/Tort x3 is just going to pile the curses slightly faster). Champion takes the rate of return on +actions all the way to zero, but other cards come fairly close. E.g. Kc/trashing boards really don't care much if you have villages (like Mining village) or cantrips (like Spy), the odds of getting stuck without Kc letting you chain a lot of stuff are pretty low, simple Countinghouse decks have near zero value for +actions.
The easier it is to fill your deck with some effect (e.g. draw, +buy, +coin, +VP, +action) the less important it is that you get that effect. For instance say I have a board with Monument/Walled village/Mining village. The +actions are not worth fighting over. Sure I wouldn't mind an early Walled village and later Mv for the end turn bonus ... but if Mass monument is viable (e.g. Chapel is out), then I want to win that split with highest priority. Villages are not quite useless, but the value is very, very low.
On the other hand if we are looking at Bishop/B-crat/Village, then it is worth a lot to win the village split 6/4.
Champion is not alone in having completely diminished returns for certain card functions. Take Kc/Scavenger. On a board without +buy or +gains you stop caring about a lot of card functions. Just about every card effect (trashing, +coins, +cards, etc.) is worthless once you have Kc x4/Scav x4. You can hit a colony a turn and the only things that do anything are attacks (e.g. Minion, Witch). Now sure normally you are further ahead with Kc x2/Scav x2 and then just pounding provinces and hoping you don't draw your Scav as card 4 or 5, but even here +coins are not worth that much. Villages have no use - you already have the assured province, you just need filler to minimize collisions (so more Scavs, estates, and coppers) or discarding cards (like Warehouse) to dump cards out of hand.
Likewise with Nv/Bridge or Pool/Monument, +cards is pretty worthless.
One of the big things I've found playing just base against strong players is how utterly important it is to know which card is key; the fewer options you have to get the effect (e.g. +cards) or something that performs a similar function (e.g. trashing), the more important it is to win that split.
