If your opponent builds a base with a lot of towers it can be annoying to win.
But keep your hopes high since you can actually outplay him and turn his investment completely useless.
By investing in alot of towers, your opponent has a strong and static defense. This means he is weak when he goes out on the map.
If you just dont attack him, you will have the advantage. If you attack him, he will have the advantage.
I suggest you to creep heavily and without fear since he will not have more units than you because of his towers. Also you can try to get a very early second expansion since he will not be able to contest that either.
Pay attention to what he is going for. Oftentimes after early towers ur opponent will try to get some air units. So make sure to get towers in ur mainbase and at ur expansion if that is the case. Feel free to use the goblin laboratoy to scout his base since u cannot send units inside usually because of the towers.
Now that u have stronger heroes and the economical advantage (second goldmine) it is just about not letting him get a second expansion. That should be easy since u have more units anways. And u need to see what he is going for. U will be able to build the units that counter him and have more items etc.
Good luck and feel free to message me if u have further questions 🙂