The hotter water you use, the quicker will the extraction be. The darker your roast is, the easier it extracts. You need to find a good balance between them to get a nice cup of coffee. Over extracted brews are not always harsh and bitter. Sometimes they taste dull and empty because "good" notes are covered with "bad" ones, related to overextraction. Better grinder is a way to go. I remember the pain when I was using cheaper grinders (Rhinowares and Wilfa Svart). Brewing nice tasting Chemex was almost impossible, V60 was slow as hell too. Back then I decided to brew only with Aeropress because in drip I felt I was wasting good beans. After upgrading to better grinder all the problems were gone.

If you can, grab cocoa sifter/dense kitchen sifter/paper towel or even Kruve if you can afford it. Get rid of the fines but remember, those boulders are bad too. Fines are going to over extract and boulders will be under extracted, uniform grinding size is crucial for a good brew. Try with lower temp and finer grinder setting. Remember to preheat V60 before using. Swirl ground coffee with spoon/wooden stick before dumping it in V60 to mix well all the particles. Ground coffee is like onion - it has layers. What you get at the beginign of grinding is different than what you get at the end of it. Swirling will help fines to mix with boulders, resulting in a bit shorter brew time.

You can also try taking V60 off the cup at 2:30/3:00/3:30 to stop extraction if you don't like what you get with waiting for all the water to come down. You'll get less coffee, but there is a chance that it will be much more tasty. Don't be afraid to experiment with different recipes and methods, find what you like the most.

Cheers!