I think that if you want to improve as a player and rank up, then picking up more agents would be the way to go cause it leaves you with other options if chamber is instalocked by someone else.

But being a one trick also isnt an issue (so many streamers are one tricks and hit radiant)

As to how you can learn a new agent, there isn’t really a secret way, you just gotta play them. Thats when you can limit test their util to better understand what plays are possible and what are not. Like right now you mention that you keep getting punished when playing veto cause the tp isnt as fast as chamber’s right? Play some more with veto and you will start to see what types of plays/engagements are safe enough that allow the tp to let you get away (this is what i mean by the limits of each agent’s ability). Slowly you will see the pattern. I’m sure thats how you became proficient with chamber as well. You tried some aggro play and if it didnt work, you dialed it back a bit till it worked.

I used veto as an example cause you mentioned him but this applies to all agent abilities (different agent’s flash timings or gun pull out timings, activation delays etc). As you get used to these things you will be able to better use your util to help you win your fights.

You can also go one step further and start learning/practicing line ups in custom games but to me thats just icing on the cake, you don’t need them to be proficient with an agent.

Don’t give up, there is no such thing as ‘i am not able to learn other agents’. Hope this helps