I go the other way and like 75/25 for juiciness.
Fat is flavor and moisture.
Maybe I'm just not the best burger maker.
If I cooked a 90/10 burger, one would need lots of beer to wash it down.
I have been continuing "Burger Experiments" on the grill. My recent favorites are simple ground beef from the local butcher. We make them really thin (1/4 cup measure then placed in a burger press). They are seasoned with Weber's Chicago Steak seasoning on one side only. I make a HOT fire, use the Grill Grates flipped so they present a griddle surface. I pre-heat the grates, then clean and oil with an oil soaked paper towel (Canola oil). When the burgers are made, we use burger papers. That makes application of the burger to the Grill Grates, "easy-peasy". A couple of minutes a side (YMMV) with a slice of cheese applied after the flip. The cheese melts and they have the most wonderful crust imaginable. Two patties on a bun with cheese! Flavor is over the top! I like a slice of Vandalia onion to top it off...
Lately I have been using 80/20.
Light seasoning with salt/pepper and cooking on a hot grill.
I flip them often.
We don't like eating pink hamburger meat, but we still like some juice and the 80/20 has been getting the job done.