Jedi, especially Guardians, are by far the most powerful combat class in a straight fight. A well-equipped soldier can hold his own (jetpack, repeater blasters, Multishot and Heroic Surge are the keys here), but if it comes down to one-on-one he won't last long. A lot will depend on the environment and the opponents. Soldiers (with automatic ranged weapons, heavy firepower, grenades, etc) will generally find large numbers of battledroids or other mooks easy to manage, especially when he's got decent fields of fire to play with, while a Jedi is be better against a small number of powerful opponents in close quarters.
The other big differential is that Jedi (or Sith...) are very hard to take down because they have access to the various Lightsaber Defense feats, and low Defense values all round are a hallmark of d20 SW. To Hit bonuses outpace Defense scores very, very quickly and there simply isn't any reliable way of beefing up your soldier character defensively, other than blowing two feats for Defensive Martial Arts. Armour, since it only works against WP damage and is useless against lightsabers, is generally only useful to make your cannon fodder a little more survivable.