WWII officially ended in 1945- 1950s so those F-5 are 70yr old jets .
M7 definitely has best hardware in fighter jets but they are expensive to run and maintain. But definitely they project power. Kenya really need drones and helicopter gunship as we are unlikely to fight conventional war with anybody. For Museveni he has to keep threatening Rwanda, Congo and South Sudan...
F-5 Tigers are from the late 50s I think. They are effective and cheap to operate for the environment. I don't believe they need anything more.
They are old indeed. Though I hear they have modern avionics. So they are not in their entirety from that era. Those newer things are indeed expensive. So even the pilots don't really have enough hours on them.
But if Uganda somehow attacked Kenya, those planes would be the first thing to be destroyed. A tomahawk missile strike or two from the US would do the job. I doubt the US and UK would sit back and watch, especially with UNEP headquarters in play.