Fair point. I would argue hat time travel needs to work consistently within the rules of the fictional universe as presented on screen though.
For my own tastes, that's the sort of idea that sounds kinda appealing in theory, but doesn't always work in practice. Or, it can work, and should work, but it really depends upon what one means by "rules of the fictional universe as presented on screen."
In
Star Trek's case there are two factors. One, especially in TOS and all the more so in early TOS, the first time it happens it is literally establishing the rules of the fictional universe. In S1 TOS, we have "The Naked Time," "Tomorrow Is Yesterday," "City," and arguably also "The Alternative Factor," though that last example is well-known to be a mess and it largely only name-checks time travel by referring to Lazarus' saucer as a "time ship" or "time chamber" and Lazarus himself as a "time traveler." Anyway, the point is that the fist time it happens, the rules are being written, so there is nothing to compare it to.
Two, the other factor, is that just because it's happened one way in earlier episodes it, in my view, shouldn't necessarily exclude it being done different ways in different episodes. "All Our Yesterdays" isn't a great episode, but the Atavachron is an original idea and therefore interesting. Its rules about travelers having to be prepared is unique to the episode. Does it matter that that's not the way time travel works in any other episode? Not to me. What brings the episode down from greatness for me is primarily the tedium of Kirk's adventure in the past. Spock's and McCoy's adventure is where the real story is.
Take also "Yesteryear." Do we know from "City" that scanning the past can cause changes in the timeline? No, we don't; in fact we see nothing to indicate that at all since Spock's scanning of the past with his tricorder is central to the plot of "City" and nothing detrimental happens as a result of it. Does that reflect badly on "Yesteryear"? Not to me. It's a rather clever extension of what we see on screen, but it's really an entirely original contribution.
"The Alternative Factor" is, among other things, an object lesson in why an episode becomes bad when there are no rules being followed. Without getting even more long-winded, suffice it say that, in my view, the other examples of time travel in TOS/TAS work, despite the differences in the way they work, even though they make up the rules as they go along.
I probably should at least touch on the fact that the beaming at the end of "Tomorrow Is yesterday" is also contrary to all other known methods of time travel in
Star Trek. Does that matter? Well, if I'm being honest, maybe somewhat actually, but on the other hand, it was original, and it seemed like they were trying to depict
something that made some kind of sense on some level to somebody. And also, if I'm being honest, I'd rather have something to think about than nothing, which is what you have if it's all the same.
TL;DR = I'm not exactly disagreeing with
@Mytran, but there are really a lot of moving parts to the idea that rules in fiction should be obeyed.