I've used a lot of Diamine inks and never found any of them to be too dry. They're mostly just middle-of-the-road in terms of wetness. Never used Soft Mint though.
So I was curious and I quickly googled some reviews. I read a batch of about 5 or 6 of them, and none mentioned the ink being dry. In fact, here are some comments I just cut and pasted from reviews: "it flowed freely", "it flowed well", "was well lubricated"... "has good flow", "average flow" "flows nicely", "very good flow" "excellent! Flows nicely". I assume these to mean that it's not too dry.
Here's a longer comment from an FPN review: "Flow for this ink seems to be high. I suspect a dry fine nib would have no issues. Lubrication was moderate in the pen tested... The writing experience was tricky due to the moderate lubrication..."
Unless there's been a change, maybe you did get a drier than normal batch? Did you switch paper? I find that my Diamine inks flow driest on Mnemosyne, and on Rhodia "R" paper (not very dry, just drier than on other papers).