When I was a kid (circa 1950's) Dad used to cook steak for breakfast every morning in a "toaster oven". The only difference between a toaster oven and the broiler in the oven was ... size. If the cut of beef isn't conducive to "quick broiling" ... then it doesn't matter if it's a toaster oven or a full blown oven ... it's going to be tough.
The amount of fat is not always an indication of how "tender" a piece of meat will be. (not talking about Kobe or Aberdeen Angus here gang) Where the steak comes from (the cut of meat) is a better indicator of how it needs to be cooked ... the fat may only be related to the grade (prime, choice, select) and not related to the tenderness of the cut .... a chuck steak is going to be tougher than a rib steak .... no matter how you cook it .....
Another trick Dad used to use ... Adolph's Meat Tenderizer ... he would dock the meat, sprinkle on the tenderizer with a little water to allow it to penetrate the meat ... most mornings ... it was slimey and "pre digested" ...
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain