Too much water and rain (as I've had here in Western NY State) can make for a weaker tasting herb. Have you had the 2+ months and record amounts of rain as we have? That could be your problem.

FataMorgana

Yes, we have had tons of rain, and now days of record heat. But that could be the problem - waterlogged leaves. Will it get better as there is less rain during the summer?

The prevailing thought is that herbs are tastier/stronger in flavor when they are a bit stressed and dry. So yes, I would expect a tastier herb as the summer progresses. Don't give up on your mint!

It has been a wild spring here. Record rain, late cold temps delaying spring growth by weeks, record high temps monday (90F) but tonight low 40's F predicted. It has been hard to get the warm season plants and gardens going.

FataMorgana

Only if you leave it on the bedpost overnight.

Sorry, I'm in high spirits. The sun has come out and I spent the afternoon on the allotment. First fresh favas and peas tonight with a big mixed salad with lots of flavoursome mint. Good gardening to all.