You're overthinking this. The fact is, having a really good kicker, as opposed to an average or above average kicker, is probably worth 20-30 points per season, and you never know when those points are going to show up. In Saturday's game, if you just switched kickers, the Bills probably lose that game. Obviously, if you switch QBs the Bills lose, too, but the question was, which is the most important position other than QB. Now I'm not saying I'd rather have Bass than Stephon Diggs or Tre White, but I do think the importance of place kickers in the NFL is massively underrated, especially in the playoffs, where the pressure is greatest and the margin for error is narrowest. For example, it's not crazy to think that the Pats would have won two less Super Bowl rings without Adam Vinatieri.
Yes, kickers are paid less than those other positions, but that doesn't answer the question. NFL salaries are not a perfect marketplace. I would argue that kickers are drastically undervalued by NFL GMs as well as fans because they don't like the idea that football games (and championships) are often decided by scrawny little kickers who couldn't catch a football or make a tackle if their lives depended on it.