About the "time crystals," how is that different from the magic time orb used to transport the DS9 crew back to "The Trouble with Tribbles"?
And here's the thing: that's not a case of using one case of "lazy" writing to defend another. DS9 handled it perfectly and so did DISCO, because the story was
not about the technobabble; that's just a plot device to set up the situation and the more time you waste trying to justify it, the less time you have to spend on the actual time-loop story. To my mind, the DISCO ep would not have been improved one bit by a bunch of technobabble about "a recursive chroniton matrix generated by a localized quantum displacement field."
Besides, seriously, does Mudd seem like the kind of guy who likes to expound on the finer points of temporal theory? Maybe he's just calling them "time crystals" because that's pithier than some fancy scientific label. I call my TV remote a "remote" because I don't know or care how it works, just what buttons to push. It's just a magic TV wand as far as I'm concerned.
The "time crystals" are just a plot device to justify the time loops. That's all.
One more example: compare "Trials and Tribble-ations" to, say, VOYAGER's "Flashback." DS9 got Sisko and Co. back to TOS before the opening credits just by evoking a "Time Orb." By contrast, VOYAGER made us suffer through endless technobabble about Tuvok's neuro-something-something before we finally got Janeway meeting Sulu, which was the whole point of the episode.
Bottom line: Sometimes "Time Crystals" save a ton of boring exposition.
(P.S. I like SUPERGIRL.)