Few questions (and a photo would have been good too). How long have you had the tree, and what preparation of the planting area did you do before planting? Do you mulch with anything during the year? Is it in a sheltered spot?

Quince blight should not prevent your tree from setting fruit - if it sets in, it may distort and mark the fruits, but it won't stop them setting, so I'm wondering if there is another, cultural cause for the lack of fruiting, hence the questions above...

Five-seven years old, 2.5 metres tall.
It is windy but near-tropical Buddleja species are thriving within a few metres.
I confess that I allowed weeds-grass around the base this year, although last year I mulched and tidied and it actually had it worse. Books tell me the fungal spores are only over-wintered in dead leaves.
Planted in rich soil with added mycorrhizal fungus.
A medlar planted the same month two metres away is going like a train.

It also overwinters on dead twigs, even those still present on the tree. The problem is much worse in damp summers, which this one hasn't been, really, though I guess it depends what part of the country you're in. Couple of links below - the first is general info on quince, the second specifically about quince blight. You might be interested in the first link because it tells you about growing conditions and fruiting

https://www.rhs.org.uk/advice/grow-your-own/fruit/quinces

https://www.rhs.org.uk/Advice/profile?pid=745