Option 3 is only true when you have a sparring partner around.
Option 1: 100% Solo form training - Not real option if you are trying to be a fighter. That's like saying "Option 1: for being a good swimmer is 100% Swimming movement training, outside of the pool" This leaves us with #2 and #3.
Option3 2: 50% solo form training and 50% partner drill training. This is actually what boxers do.
Take a look at videos of people's 1st day at the boxing gym. You'll see things similar to forms training. Like locks of correction of stance, structures, and lots of practicing the same thing.
There are tons of solo boxing drills. The only difference is that with forms you are practicing way more techniques than what boxers train.
Option3: 100% partner drill training. No one does this. Why? Because what are you going to do if you don't have a partner to drill with? Not train? Of course not. You are going to work on your solo drills, which is like doing the forms with the exception you pick 1 thing and really drill it to get it right. Martial art is going to be different because there's a lot "doing 2 things at once" in martial arts.
For most people the most difficult thing about martial arts is learning how to move in different and uncommon ways. Most adults who take kung fu for the first time look exactly like this. How many techniques do you learn in Martial arts in comparison to boxing?
Most common statements that I've heard from adults is that it's mentally challenging just to get the body to do what you want it to do. Because of the complex movement people are going to spend a lot of time just learning how to get their brain to better communicate with their body.
You won't be good at partner drills if you can't do the movement or if you have bad structure.