I'm not talking in general, but for that particular fight. Sonic Shadow's animation will always last for the whole duration of Meteor attack while TS, even if perfectly executed, might end too quickly. If that happens have fun being launched in the air at 1 HP while the boss teleports at your back and kills you.
Guarding meteors isn't a 100% safe option even with Second Chance/Once More because they occasionally hit you at random intervals and from different directions, which can bypass those abilities and get you killed.
You should always run far from the boss before reading shotlock so his teleporting around shouldn't bother you at all so the increased charing time is a minor disadvantage.
Lastly, Sonic Shadow will deal more damage than TS even factoring his -25% dark resistance, which is extremely useful during the Curaga spam phase, while TS will just cause him to dash after being hit a few times, reducing the overall damage.
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