These is my opening range for 6max. You should be stealing from the BTN with a wide range.
UTG: 22+, AJs+, AQo+
MP: 22+, ATs+, AJo+, QJs+, KJs, A2s-A5s
CO: 22+, A2s+, ATo+, 76s+, KTs+, QJo+
BTN: 22+, A2s+, A2o+, 76s+, K9s+, Q9s, 98o+, 86s+
In the SB I'll steal with the CO range. When I am in the blinds facing a single raise I generally try to avoid calling (although some situations clearly warrant it like setmining vs EP nit opens) and either 3b or fold instead.
For me the example you gave above is a fold, you're right, the nits range crushes you.