A real-time battle with another player is always exciting and complicated, and there can be only one winner. If you think about it, having a 50% winrate in battles is really a normal battle stat!
Don't forget to enhance your troops by upgrading their stats and abilities, and you'll find it easier to score a win! You can upgrade your troops in your base: for example, in the Command Center. You can learn more about upgrades here.
It is also important to note, that it isn't very secure in terms of strategy to rely on one particular kind of troops. It is the combination of different types of troops that raises your chance of success. The thing is, different units are adapted to face different threats and fight most effectively against the troops they are supposed to counter. All units possess special abilities that fulfill their potential only in combination with those of other troops. If you rely solely on your infantry squads, your overall damage will never be as high as it could be in case of cooperative use of tanks, jeeps, snipers, rpg-units and basic infantry. Leveling out the development ratio among all of your units is always a good option. In a situation when player, for example, has an advanced tank or marine squad and his other units still lack a lot of upgrades, it can be difficult for him to oppose more balanced armies. And don't forget about tactics; it will definitely help you to gain an advantage over stronger opponents.