Depends on how much of a nerd you are. I think the standard level of analysis uses OPS+, which is just on-base (batting average plus walks) plus slugging (how many bases you're getting when you get hits) as a function of league average (100 is league average). WRC+ is similar, but it includes a park adjusted factor.
I think some baseball analytics go a bit overboard with it though, because guys fill useful niches even if their OPS+ or WAR isn't necessarily special. For example, a guy who has an OBP of .350 with speed but zero power is a great leadoff hitter (such as Steven Kwan). A guy who is awful defensively but can hit 35 HRs a year and get a ton of RBIs is still a useful cleanup hitter (such as Nick Castellanos). WAR usually represents it pretty well but it can overrate or underrate niche players with specific roles that WAR either likes or doesn't like.
On the Pirates, I think Hayes is a terrific example of that, especially in his 2022 season. In that year, he only had a slash line of .244/.314/.345, which is a clearly below average hitter (88 OPS+). However, WAR absolutely loved his defense, to the point where he finished with 4.4 WAR in 136 games. That's insanely overrating him, he is simply not as good as his WAR suggests in that year. I think Triolo is another guy on the Pirates who WAR overrates due to his defense.
Kwan has a SLG of .419 which would put him behind only Cruz, Bart, Reynolds and Cutch on the Pirates so that isn't exactly singles only.
the whole skenes/merrill thing is a bit perplexing to me since skenes has better numbers than the cy young candidates and merrill isnt close to being an mvp candidate
Skenes has as good numbers as Sale and Skubal, but the argument there is the same as with Merrill: there is value in having started the season vs. May 11. For instance, Sale has 2.38 ERA and 2.08 FIP, Skubal has 2.39/2.49 and Skenes has 1.99/2.48 so very similar in FIP and similar in ERA. However, Sale has 177.2 IP, Skubal 192IP and Skenes has 131IP. Those 46+IP and 61IP over an extra 7 and 9 stats are pretty valuable.
Similarly, Merrill has been playing above average defense at CF which was a new position for him and would be the best offensive Pirate if he was on the team for the entire year. If he started the same time as Skenes, he would be losing 137 of his 582 plate appearances. Losing 23% of his plate appearances would certainly impact how he is viewed, why wouldn't that apply to Skenes?