Dulce De leche as a macaron filling
I use dulce de leche as a filling or topping as well, but you are right, it is a bit too sweet, so I tone it down... one way to make it milder is to incorporate some cream and a bit of melted dark chocolate, but you cannot just mix it in...

Leave the dulce de leche in the fridge overnight. Pour off any liquid that separates out. Mix in a bowl to smooth out any lumps. In a separate bowl, whip up some double cream (ratio 2:1:0,3, dulce de leche:cream:chocolate) to stiff peaks. Add cream to dulce de leche and beat until combined. Melt the dark chocolate and stir into mixture. Refrigerate for about 30mins so the melted chocolate in the mixture can stiffen up a bit.

It's delicious and not as sweet as pure dulce de leche at all!