I wouldn’t call Skadi OP, per se. She is a Big Four support, however, and one of the only two servants in the game that can charge an allied NP by 50%, which makes her extremely valuable for farming. Her NP has a 1-hit evade buff, so she can use that to protect the party against NPs, if you can charge it quickly enough.
For Hans/Saberlot, your best support options would be either Caster Gilgamesh (if you want to go all-in on arts crits) or Tamamo (the best arts support in the game). Merlin is always great for his party invul and passive star/NP gen, even if his buster buff isn’t being used. Of course, Waver is good in every team, as well.
Arts teams work better in longer battles, assuming you can prevent NPs from one-shotting you (Mash+Tamamo should be able to stack defense enough to reduce damage to zero on enemy NP turns). Quick teams are more about trying to kill an enemy before it kills you, which is where Skadi excels. In the long run, Atalante is one of the best servants for double-Skadi NP-looping strategies, which become possible if you get a KScope (or a Waver).
In short, Skadi will be immediately useful for buffing your Atalante and Achilles’ damage, plus being super awesome for farming via her NP battery, but will become even more valuable as your roster expands, eventually allowing for the most reliable 3T farming teams in the game.