Oh, i forgot about the Legendary Lost Sectors :D but yeah, as of right now they are only possible with a Team but like i said there are other Activitys that are possible Solo for Leveling up (Strikes, Gambit, Banshee and Flashpoint for example)

They are getting so -blam!-ing boring.... after 2 strikes, I am bored to death. Gambit... unplayable since the matchmaking is finding all the morons to put in my team. Just no fun anymore. I really wish I could get a refund

You have a Point there, it's understandable that you would love to get a refund and this time i did most likely the right decision and i didn't bought Shadowkeep and any Season (Undying, Dawn, Worthy). The only thing i do to Level up is Flashpoint, Banshee and random Prime Engrams and Exotic drops. When i'm done with that then i play a different Game or go offline completely. D2 will never be like D1 and Trailers can be good and everything but i know that the actual content is trash, that's why i never trust Trailers. I regret that i bought D2 because of year 1 in D2 but Forsaken was ok