First of all, welcome home. Every AT can solo, some just not as well as others. Controllers might be the hardest, and when the game launched it was even harder on controllers until we got our pets. Defenders can be slow since they don’t put out tons of damage, but their power to heal, buff and de-buff makes it easier to survive. Sentinels are good solo characters for new players. They may not get the love in the post 50 game, but they are a good ride to 50. Brutes go without saying. One of my favorite solo characters is my Dark/Dark stalker. Tons of damage and I can stealth through certain parts of the mission if I want to.
It’s understandable why people solo given a limited amount of play time and other factors. However don’t miss out on one of the great strengths of this game, grouping. Given all the AT’s and different power sets, no team is ever the same and always an adventure.