That is truth that NG sihil is much better than skellige sihil due to additional control options - bronze locks and leader ability - and well played sihil is very strong aechetype. And from my expirience unwinnable matches for sihil are Ketullis and bear ritual, and almost unwinnable against NR grace knights and syndycate bounties and lined pockets due to candle. Other matchups are possible to win and depend on skill and good draw.
There is one truth about sihil though- sihil is way stronger against control oriented decks than against greedy decks, pointslam is somewhere in the middle. So if You just play heavy control oriented deck on Your own and enjoying fact of wiping out opponents board like warriors, pirates, elves or many others , sihil will do the same to You. In conclusion - if You dont run control deck with only domage no boosts, You have chances against sihil or even advantage against it, the rest is decided in Your and opponent skill. But if You run control deck on Your own and than complain on sihil that exisis, it sounds like a thieve screaming: Catch the thieve, because sihil is doing the exackly the same oppresive thing than You, just does it better.