Phase weapons and phasers.
I don't see any "succession" there, really. It rather seems that the very same guns were given two different names in two different time periods. Why improve on perfection? The revolver hasn't changed noticeably in the past two centuries; the difference between Archer's sidearm and Kirk's or Picard's is not evident on screen, and at best would be something even more subtle than the transition from black powder to modern smokeless in revolvers.
In contrast, succession between the plasma guns and the phase guns seems a rather arbitrary claim. Armies went from crossbow to gun at one point, but the gun could hardly be considered an improved crossbow, and there were no intermediate steps of gunpowder-powered arrows (those were a different weapon in a different culture that never had crossbows) or tension-string-fired lead slugs. "Steady evolution" really is an unlikely occurrence, and actually one of the concepts that detracts from the understanding of the theory of natural evolution, because "punctuated equilibrium" is so much more easily observable... Both steady and unsteady development usually take place, and choosing just one half of the model and turning down the other is an artificial and very probably inaccurate way to interpret development.
Doesn't mean phasers couldn't be advanced plasma throwers. But plasma is such an impractical weapon from the get-go (essentially, you just blow hot air on your opponent). Why should the potent weapon of the hero be based on a scifi concept we'd do better without in the first place? Especially since scifi needs identity, and Trek has generally been good at having some, say, with its prominent use of teleporters as an everyday tool as opposed to every other tome's use of it as near-magical special technology.
Really, since Trek has turned teleportation into a household technology, and supposedly uses "phasing" for it, one would expect a host of spinoff phase technologies that would radically change the Trek world and make a clean break from the technologies of the past. Phase pistols would be an obvious candidate. I mean, steampunk is no doubt a valid way for technology to proceed, but we know from history that the adoption of electricity can produce a vastly different and discontinuous world of technology. Adoption of phasing could mean a similar discontinuity, and would really help explain how the Trek 22nd century can be so amazingly advanced already.
Timo Saloniemi