P.S.
- Can'tanswer in comment section, as my browser seems too old for modern day SE java script, or whatever, so do it this way.
If each of them is in their home system, then with basic preparations they are quite set to repel K2 backed invasion even with 1% of K2, if their tech levels are more or less comparable otherwise. In case if a smart matter is not possible, as an example and they are stuck to previous gen technologies stack. As transfering sufficiently big invasion forces to supress other system, and arrive in some reasonable time (fraction of ligth speeds) with no invisibility in space and interstellar medium(hydrogen and dust stuff) is one of the things K2 power alone may be not so sufficient.
So it then even more so a case of cold war and who gets to next level tech first, who is the smart, who is the good boy. And then even if one is K2 and another are K1 but with smart matter - K1 has good chances, not even talking they have then the means to become K2 soon (but they may prefer to keep it secret, so, they may be reason for them not to show atypical growth)
But okay it a different tricky topic of interstellar warfare, and space warfare which is a deep rabbit hole, and quite pointless how it depicted in movies, or most of scify stories, and it requires, just demands, a certain tech levels.
Which K1 can easily achive, in my opinion, but it hard to create an advantage in another star system even with K2 - just for reason it requires a lot of energy to just deploy/deliver means of attack, and for them it is cheap to set means of defence. 0.1c attack speed vs 30km/s deplyment of defence means is a difference of 10^6 times of energy spent. And attacking side has to overcome the difference. Hacking and alike, sneak invasions, inside job etc may be a better way to invade.
Dyson beams, eh, so so - never bothered to consider their potencial efficiency at such distances (ly's) but one gets 10% of K2 at best with lasers and they have physical limitations how good a beam you may have, meaning density of spot at arrivial. And as an example a 2 ligth second spot is not sufficiently strong to kill random targest blindly all over the system and that is K2 energy.
Relativistic kinetic stuf is better, but it easier to detect them from the distance, and more importantly deploy means of their destruction (some dust clouds, foil sheet, etc, which works for a beam as well) so it also not a wunderwaffe. But okay it offtopic for this q. You may look at some of the other answers of mine https://worldbuilding.stackexchange.com/search?q=user%3A20315+realistic there are some
Specifically this one: How does a spacecraft attempt an intercept course with a hostile one realistically (Part II)? read the premise of the guy, in that one I tried to look at how a more or less a proper star system defence system should look like, and it decent as for internal law enforcement so as defence against incoming forces - fusion tech, nothing fancy like a smart matter. This one as well similar topic Fleet tactics & strategies in a hard sci-fi setting with near light speed weapons, ultra hypervelocity kinetics, realistic sensors, and torch ships and there can be more of those mines and other ppl.