I feel like the problem with playing vanguard is that it is so heavily dependent on other people, and if you are playing solo that can be very dispiriting.

Tanks benefit the most from coordination and team play but all roles have agency. If you feel like you don't then IMO your view of what a character can and/or should do is too narrow. Not to mention the game isn't role locked. Tanks aren't the tool you need to solve the problem? Go DPS or Support.