I haven't played it in a long time, so you probably already know more than me. I'll give the game a few goes now and give better information afterwards.
One of the game modes involves going around all of earth and conquering it country by country. You have a spaceship fly around your units, but there's a limit to your arm size as you carry them around. That might explain why the Hierarchy don't just send all of their forces to one spot. I imagine that they're so large that they attack multiple planets at a time with different sets of forces from various planets. After all, I imagine that some of those 100 billion are pretty far from Earth and would be impractical to send all the way over there. Maybe in another game, there will be 100 billion planets' worth of units in an army.
The Masari are closer to playstyle B in my opinion. They don't have units that are as part or powerful as other troops in Novus and Hierarchy, but they can replenish an army after attacking much more quickly, since fallen vehicles spawn an infantry unit whose machine can be rebuilt. So, they are good at making quick, powerful armies, as well as keeping their units alive for a long time with good play.
The Hierarchy are definitely option A. You have to get a giant Walker to spawn units from or just attack. Most of their troops are pretty tanky, I remember that the Hierarchy Grunt beats basic infantry from the other 2 races no matter what stage of the game. Their late game units do a lot of damage, too, like their Flying Saucers and Phase Tanks. Walkers themselves when upgraded are by far the hardest to kill. Mumakil have about 10% of the lifespan of a Walker. Get one with full attack upgrades and just send it in behind some other units. You can keep spawning troops from the walker even once it's moved far from your base, so you can spawn more troops inside of the enemy base. The best tactic is to spawn Brutes, who are building killers, or just make grunts to protect the Walker as it steps on all the enemy structures to instakill them.
Novus are a lot like Men in BFME 2. They have weaker, spammier units to start but can get really powerful troops later. Antimatter tanks are so great with their deep voices and awesome attack style, planting bombs on enemies that explode a little while later. They can also set up poles around the map that enemies can't see or attack which allow them to move around the rapidly map by teleporting to each pole. They also get 2 powers instead of one, an EMP to freeze units and a Black Hole to finish them off.
The only thing that might seem lacking is the heroes, since you only get 3 per faction and some aren't as good as other to me. Melee heroes are particularly useless against large armies. I always like having a leader unit for my army, but there aren't any that really support your soldiers. They're just stronger, more expensive units. At least they do have some fun powers and are actually really strong. The 2k heroes are all the best.