Is it possible to increase strength/mass ratio without gaining excessive weight?

Yes, it is possible to get stronger without gaining mass. Strength is largely neuromuscular, so increasing your nervous system's ability to send signals and recruit motor units can help you become stronger. Mass can come from training volumes and caloric surplus, but if you manage them correctly, you can still focus on strength without gaining a lot of mass.
 
Transcript: "Yes, it's possible. Strength is largely neuromuscular to your nervous system. So you're increasing your nervous systems ability to send a signal to the muscles recruit motor units and get those things firing. Mass is going to come from training volumes and also a caloric Surplus in terms of you're eating. So if you're smart about your eating and there's a skew towards strength training, lower volumes, higher intensities, higher loads, you can absolutely get stronger. And if you look at some of the world's strongest athletes powerlifters Olympic lifters, Have to meet weight classes and the amounts of their strength, to body weight. Ratios are pretty impressive and even athletes were maybe there's less of a strength component swimmers Sprint Runners where they have to demonstrate Force within their sport. But they don't want to carry a lot of mass and have a lot of cargo on their body to have to carry as well cyclists as well. Power 2 kg ratios and things like that. So absolutely strength is neuromuscular. It doesn't have to come with a physiological change in your mass. That can be helpful but you want to manage that depending on what the goal is."