I think Vx is a fixed speed for still air but if your obstacle was power lines then you don't have to factor in descending air off the obstacle so headwind would benefit your climb angle if you were slower. As a crop duster sometimes I decided to go over or under the power lines depending on my climb rate. It didn't really matter much but with normal flight operations going under the lines was not an option. Flying for the airlines we don't think of this because we have different rules. It is fun to climb straight up in a J3 with 65 HP and make multiple landings without having to fly the pattern though. Not much point in it except it was a lot of fun.
Yes, Vx is a speed, not an angle, but for a J3 cub to have a 90 degree climb angle on those days is quite impressive. We watch that F35 at Reno every year at the air races do that flip loop and climb vertically with zero airspeed. Now that is angle of climb profile. Lots of factors fit in to best angle of climb.