I believe that overall statistics is a combination of Veterans and GS. While Eithne has all the tools to properly hinder a GS deck but not so much to a veteran deck. Artifact Compression and Mandrake are useless to a veteran deck and it isn't that difficult to play around scorch as long as you pay attention to the sequencing of your cards.
That's the fundamental problem: you can play hate against Greatswords, but they're bad against other decks. If you have too many copies of Artefact Compression Mandrake etc, you might beat Greatswords but you'll lose against the rest of the field. Veterans is an example of these "other decks". It's conceivable that a teched out Eithne deck squashes Greatsword, but the overall win rate vs. Crach is an example of how bad the deck is.
Artefact compression is good against alchemy (deny resurrecting witchers), NG handbuff (spotters or even Golem/Knight/Assyre/Mantikore), deathwish Dagon (Dao), Henselt (Ronvid), mulligan ST (15+ points officer), Harald decks (axemen, Derran). In the worst case you compress your own spy for 11 points.
Why do you think Coral is in every SK deck?
Against all the decks you mentioned the only deck that Artefact Compression is actually good against is NG Handbuff. Look carefully at what Compression does against the other decks:
Alchemy: 3 points (!), you don't even deny Viper Witchers because they have three of them, plus even if you deny them they can still resurrect Vicovaro Novices which are almost as good.
Dagon: 4 points, and ditto. They have more than one Dao, and even if you deny all their Daos, they still have Archespores so their Griffins etc aren't terrible.
Henselt: Ronvid is great but not essential to Henselt; they have lots of crewmen.
Compressing your own spy: what if you didn't draw spy / mulliganed into Artefact Compression in a short round 3 / etc?
Remember you are playing a silver card, and silvers are expected to hit 13-15 points without too much trouble (e.g. Ida, Jotunn, Ronvid). Coral is in every SK deck because it is not Artefact Compression. It's a 5-point body on top of Artefact Compression. Mulliganing into Coral in a short round 3 is usually not bad. Mulliganing into Compression can lose you the game.
UPDATE: also I think it's gonna be worth waiting another meta report, as season start and 3600+ as highest tier is not always very accurate regarding the true power levels.
Crach has been dominant in the other two meta reports too.
https://gwentup.com/report/18/20 - 3900+, Crach 53.7% win rate, GS 55.3% win rate
https://gwentup.com/report/18/19 - 3900+, Crach 54.4% win rate, GS 54.5% win rate
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Maybe make Light Longships no longer Dimun units and so not be summonable by Pirate Captain.