In which ways is Duality better than Activity?

[shakealittle]

and activities gives too much polr "hits" because activity partner's polr is their 7th function.

Your dual would be using more of your 4th function than your activator. So you would get more polr hits from your dual than your activator, in my experience anyway. Your activator at least keeps an eye on your 3rd function unlike your dual which ignores that function and I would think we are more concerned with our 3rd than our 4th. I would get way more Fi assurance from an IEI than an EIE.