I play GW2 on a GPD Win Max (1st Gen) which has way lower specs and it works great. In Dungeons, Fractals and Raids I can even set Graphics to best Appearance. So I think the Steam Deck should have enough Power for high Details in the open world.
As the Screen just has 1280x720 px (which is absolutely enough for a small screen) it needs way less graphics power.
I use "Controller Companion" for mapping the Gamepad. Just enable "Autotargeting" and "Snap Ground Target to Current Target" in GW2 Options, in Contoller Companion map Joysticks to WASD/WQES and Cursor movement, RB/LB or RT/LT to Mouse Buttons and whatever you want the remaining Buttons to be and have fun.
Yes, Please!
