Where does a master solo flawless lost sector completion land on a difficulty scale?

I did my first solo flawless master lost sector yesterday, and I was wondering out of all the activities in the game, how hard is it? I consider myself an above average PvE player, and want to look into doing solo dungeons, raids and more grandmasters. Since I’ve completed a master lost sector, I feel pretty much prepared for anything. Am I being too confident or am I right? Any advice/challenges for me to do next?