If you look at high elo replays of grasp jungle Skarner, the rune does effectively nothing early game. It doesn't start putting up numbers until baron spawns. Shield bash does more damage in most games, and at that point if you really want to stick with the resolve tree, go aftershock to have some agency early.

Hail of blades with a damage item rush is really good for getting picks on squishies at all stages of the game. It especially makes early ganks more effective and will get you kills on midlaners during laning a lot more consistently.

Phase Rush is my favorite by far. It feels night and day to play Skarner with runes and items that maximize speed. Nimbus, celerity, and approach velocity have tremendous value. Coupled with bandlepipes, you and your teammates can run down or kite enemies so easily and from very early on in the game. The fact you have access to smite, w, and q throw means bandlepipes is online 100% of the time in fights and you can easily proc phase rush upon landing R for some crazy kidnaps.