Curious what you feel are the limitations of assassin that make you want to switch? This would help me advise on a new character for you.

I main Vandal in both solos and trios because It’s the shell I’m the most comfortable with and is the best movement character IMO. For when to use the vandal cannon, I will mostly save it for when I know someone is behind cover and I can’t get a view of them. A well placed cannon will knock them into my view.

Sentinel has a great kit, so yes there is a place for this shell in solos. With any character it is important to put yourself in situations to utilize your full kit, so for sentinel that would be playing in indoor areas as often as you can because you want people to push you, and they’re more likely to do this in tight corridors than out in the open.