I think "Kelvin timeline" is really clumsy, and doesn't really work or fit. It's also probably the best and only possibility in-universe.
But I sure don't use it when talking about it (it's "alternate universe" formally, "reboot" when being objective, or JJverse or something equally wrong when being informal). I mean - I guess Bob Orci was probably the one most responsible in defining it as an alternate timeline, being the only major creative force who was aware of "canon" in the beginning.
Overall though, I think the extremely muddy definition of what this Kelvin timeline actually is (it's not a full reboot - but by god it doesn't work as a regular "alternative history" either), is part of why these movies don't have a clear place in the Trek universe anymore.