And yes, the idea of switching insignias every few years is silly at best. One doesn't need to have an alternate theory to have an opinion on your theory.
But they did
switch insignias every few years. If you think that's silly at best, then your criticism applies to Gene Roddenberry's and Nicholas Meyer's choices.
Obviously, Starfleet's crest and symbol is the (mylar coated) arrowhead we've seen in many subspace video transmissions, courtrooms and on the hull of Starfleet vessels like the Enterprise
or shuttlecraft (since the one in "Metamorphosis" was obviously powered by antimatter, it appears it had warp drive capability, IMHO).
Apparently, for the uniforms it's different. The receptionist in Commodore Mendez' starbase office
(still) wears a delta insignia very similar to that of the Enterprise,
in contrast to the flower insignia that's already around.
By the time of TMP the whole thing has changed again. All Starfleet personnel (e.g. Starfleet Admiral Kirk) now wears the delta overlapping a circle.
By the time of TWOK, 15 years after "Space Seed", the Starfleet insignia (e.g. Starship Reliant) has changed again. Now the delta is overlapping a rectangular shape.
And what's so silly of honoring the accomplishments of a particular starship (or two from TMP on) by adopting its insignia for the whole fleet?
is by Gene Roddenberry's definition (whether you like it or not) foremost a vessel of scientific exploration.
In our world we honor scientific achievements with the nobel prize, so I'm unable to see what's wrong doing something similar in the future (should we ask the nobel committee to stop this price as it discourages other scientists who didn't make it?).
Alternately, if you regard it from a military point of view, adopting a starship (insignia) that has impressed / defeated Federation adversaries for the whole fleet, can have a strong psychological effect on such adversaries. They encounter another Federation starship but the insignia they see on their communication screens has a clear message: Don't underestimate us, we are of the same breed as the Starfleet officers you previously encountered (considering the humiliation the Romulans suffered from the Enterprise
, adopting the "NCC-1701" for the Enterprise-D
had a nice touch to it).