Same, I have eczema and unfortunately my scalp is dry like the Sahara, so it takes a while to get greasy, that said though, it does go a bit lank after a couple of days of styling and if I use product it looks dull by the end of 2-3 days. I do agree with the OP though that unwashed hair can stink, I think it’s more noticeable with warmer weather. Also if cooking onions I can’t stand the smell clinging in the hair so I would have to wash it that night. I love onions but the cooking smell is rank.My hair literally doesn't start getting greasy until 5 days after washing.
I can wear it down on day 4 and it looks (and smells) freshly washed.
But my skin in general is VERY dry and dehydrated. My legs go scaley if I don't moisturise them. My face is an ongoing battle of keeping it moisturised.
So it is definitely an individual thing. Not everyone gets greasy