Guild Wars 2

I just came back to GW2 after a long break and am trying to understand how this system works.

It seems like I can spend points to learn a skill that I already have unlocked. The screenshot is before I upgraded.
And after I purchased it nothing changed.

Am I being ignorant and not realizing how this works? or is this a bug?

Great I just started playing 2 weeks ago and I choose mesmer randomly and was enjoying it. Now I hear that it keeps getting nerfed, I feel like all the struggle I went through on lower levels are for nothing now if they keep on nerfing mesmers. Leveling is so slow for me as a mesmer and now it’s probably going to be even slower and less rewarding.
Not the best way to keep a new player playing this game.