[... much silliness and nonsense]
There are two quite different meanings of the symbol "c" [#], which have
confused you (and myriad other newbies and wannabes).
* c(1) is the speed that appears in the Lorentz transform.
* c(2) is the vacuum speed of light.
Note that c(1) is the limiting speed for timelike (massive) objects, not
c(2) as you seem to think. c(1) is locally invariant, and is the only
speed at which massless objects can travel.
At present, to the best of our knowledge c(1) = c(2); the limit on the
mass of photons is extremely small, but is not zero. This numerical
equality seems to be rather a coincidence, as these two meanings are
QUITE different. If it should happen that photons are not actually
massless, then c(1) != c(2) and lots of physics books would have to be
re-written. Folks like you would no longer get confused by this
particular subtlety (but of course many others remain).
[#] Due to the historical accident of Einstein using
electrodynamics to discover Special Relativity, while
logically their relationship is the other way 'round:
SR is geometry, which is much more fundamental and
pervasive than electrodynamics.