Yes, K,M,P,T are expensive if compared to Value booked in advance (since Value can be had in any class with a fixed add on). If Y is 20 times the cost of an R, then T is 10 times R and K is 14 times R.
But in more normal fare classes, like S, the difference is not that large. A T-fare compared to a theoretcial "S with Value" (which doesn't exist) is some 30% more expensive. Not cheap, but at least 100% points. And that is my point - how can a Finnair loyalty program work when customers to Japan pay a premium to fly Finnair and gets less awarded?