I'm starting to think we need some sort of reboot spectrum so everyone's OCD need to categorise what is/isn't a reboot can be satisfied.
I mean, what are the options?
HARD reboot: eg. Battlestar Galactica. All other realities/timelines scrapped and have no bearing on new incarnation. Someone pushed the big red button and did an honest to god REBOOT.
WEAK reboot: Now this is where it's trickier territory, IMO. Kelvinverse used time travel hijinks to fork off of the prime timeline. It's not the prime timeline unfolding differently, but an alternate reality. But effects in tampering with time in the prime universe have been shown to ripple thru the prime reality. Which, if we take the alternate reality thing at face value, it means even if Our Prime Heroes or the 29th Century Time Police shoot back in time and correct things in *their* reality (stop Nero before he starts wreaking havoc in the 23rd Century), the alternate reality still plays out - we just don't get to see it, except in the Kelvinverse case. Which mean in say... First Contact, The Borg went back in time, created an offshoot reality and assimilated Earth in 2063 AND were stopped in the prime timeline by Picard and co.
Ok, that's starting to get messy... That last bit is more to do with how time travel works in Star Trek and less about reboot definitions.
So, they get to do what they want in the Kelvinverse, but it's not a reboot of the prime timeline. That still exists independently. SO, WEAK reboot.
And now we have Discovery where the producers have stated it does take place in the Prime timeline. No offshoot. Therefore it has to be reconciled with prime timeline continuity if it's NOT a reboot. Hence, we're getting the term "visual reboot" thrown about to compensate for the obvious incongruity between Discovery and TOS.