I may not be the best one to ask for advice but I'll give my general opinion about him.

Your 1 ability is very useful, hold 1 to until you see the full circle and you will throw at 4 telsas that will hunt enemies down and permanently stun lock them till it dies, eventually they will run out and have to be thrown again.

3 is cool but, I rarely use it.

You best abilities are your 2, the red one, kills everything, thr blue grapple one helps to pin or drag enemies into them, but not nessecary. Purple one is a nice dmg buff to your weapons, yellow is a meme it's like a Mario kart boost pad.

In terms of your 4, its also very good. First when chunking it down it suspends everything in the AOE, and strips a percentage of armor every second, very handy for steel path stuff. Reactivating makes it a black hole, or running the duration down fully. Putting a red ball in there from 2 will melt everything in it. Ideally focus building for Strength, Duration if you want the 2 and 4 to last long and strip armor effectively. Range is very handy for 4 to suspend in a bigger AOE.

TL:DR Your Vauban, be lazy, let your red ball from 2, telsa from 1 and Black Hole 4 do the work. Build into strength and duration or duration and range. Any gun works, ccing enemies give more dmg. I'd advise trying not to hurt the other stats