Smaller outfits simply need to do what I've been doing in EVE Online for seven years; make good use of force multipliers.
Pull MAX suits. Use upgraded MAX suits and have a dedicated, fully certed engi keeping them alive. One MAX suit is easily the equal of 4-5 enemy especially one with engi backup who knows when he's taken too much damage.
Speaking of engies. Claymores are one of my favorite tools. When you jump on a base and start taking it as an outfit, have your engies jump into their claymore outfit, and start marking chokepoints and entrances with them. Then they can switch back to whatever class they want. Claymores don't disappear if you swap classes, so use them liberally.
Light Assaults with C4. Place your LA up high near chokepoints if possible. Tell them to hold their fire until the enemy is past them and shooting at your HA, then have them open up on their rear with C4. In the military we use this tactic of drawing the enemy in, then surrounding them.
Grenades. I make the vast majority of my xp every day from grenades. If you find yourself heavily outnumbered, then you're absolutely 100% guaranteed to find your enemy all bunched up in small pockets. Fill those pockets with lethal death pinecones.
There are also a few other ways to multiply the force of a smaller outfit, but I don't want this to turn into a TL
R post.