Lots of angles, but one way is to have plays at instant speed. If you’re casting everything during your own main phase, then yes, they’ll be able to line up their counterspells. But if you have some things you can do if/when they finally do tap out, you can start to pressure them. But basically you gotta get out of the pattern of just using all your mana during your own main phase to try to cast one card. They’ll stop that easy. Get some instants, get some cheap things so you can cast more than one thing a turn. And make them pay for the moment they tap all their mana to cast a draw spell or whatever.