1.Skaven Ambush is way stronger than LS because it allows one-sided reinforcements and it's trivially easy to buff it to near 100%. It's also the default attacking stance so you might get it even if you don't want to. Combined with all the mid-range firepower Skaven can bring to bear this is just overkill
-make it dependent on Skaven corruption (should only be an option at 50%+ corruption), remove reinforcements and cap the chance at 50%. Also, give Skaven a "normal" attack stance
2.Skaven settlement upgrading on capture sidesteps the growth nerfs from the last patch since you can still just pump a captured settlement to max level within the first 10-20 turns.
-restrict to T3 intitially, unlock T4 and T5 when you have researched two and four of the Greater Clan dependent research topics respectively (the ones that require a Greater Clan specific building to unlock)