I don't agree with the bolded. You may have other points about usage etc. but there is no sharp change in his performance. He improved gradually and slightly to the '15 season and then fell off gradually and slightly since. The difference from his best to his worst season is not all that great if we make a bit of an allowance for his injury last year. Otherwise he has never been either very good or very bad. If he rebounds to his best he isn't an Enstrom replacement. That would be a #2. He might be a 2nd pair Dman if we get lucky.
Wiercioch has also fallen off a bit over the last couple of years. I can't go into sufficient detail to determine if there is a usage explanation for that or not. Over their careers Wiercioch has had better numbers in every year in the NHL. He has done that while playing only about half as many games and fewer min/gm.
I'm not making any attempt at an exact comparison between the 2 players. A superficial look at some statistics says that Wiercioch has been the more effective player. That is sufficient when Kulikov is making five and a half times as much money to know that there is a market inefficiency, on at least one end, more likely both IMO. Wiercioch is a bargain and Kulikov is overpaid. Are they equal in value? I can't say that. Should they be at 5.5:1? No way.
What I'm finding humerus about the Wiercioch Kulikov debate is that Wiercioch came into the league as basically Logan Stanley. An oversized guy with big questions around skating and mobility. While Kulikov came into the league as everyone's favourite d prospect making just about all mock drafts top 10. A strong skating, mobile puck mover with above PPG junior scoring numbers. Maybe how they are currently seen is a carry over on how GM's saw the 2 players in the past, but Kulikov has more pure talent however it still remains a question if he can re-find his game at age 26.