The huge problem with that is Kirk's opening log entry. He says he has picked up "the call letters of a vessel that has been missing for over two centuries". This necessarily means he knows exactly
what sort of a ship the Valiant
is - he must
have looked it up in order to connect the call letters to the missing-for-200-years information.
If he has thus learned that the Valiant
is an insystem vessel limited to sublight speeds, he is not permitted to continue with his next remark: "Did another Earth ship once probe out of the galaxy as we intend to do?" No way, no can do, makes no sense.
He could say "Did another Earth ship end up here on the galactic rim before us?" safely enough. But the act of "probing" poses specific requirements on the performance of the Valiant
. If she lacked that performance, Kirk could not say the words.
Sure, getting the Valiant
from Earth to the Barrier might be a feat a hundred times greater than sailing a seven-meter launch across the Pacific. But there'd be nothing theoretically impossible about that - it would just call for more favorable winds and currents, slightly better luck fishing, slightly more rain for fresh water and so forth. But if the Valiant
lacked the vital basics, if Captain Bligh only had cork jackets for his heroic band of eighteen rather than a launch, then the feat would be truly and blatantly impossible. Kirk would be speaking of divine intervention (or wormholes) rather than of "probing".