I assume most people do not think about this flaw or if they do it is merely hand-waved away.
Opinions?
My opinion is that Kenku are one of the most poorly thought out races in 5th edition.
Even if we put aside the whole creativity/speech gimmick, Kenku are one of the worst balanced races in the game. Their racial features are practically nonexistent compared to other Dex races, such as halflings, elves, goblins, or tabaxi. And then, of course, there's the creativity/speech gimmick.
The most frustrating thing about Tengu is that it's rather unclear what "incapable of creativity" actually means in practice, and many interpretations seem to simply be inconsistent, self-contradictory, or so constrictive as to render the race unable to perform basic adventuring tasks. For instance, we're told that they can't be creative, but that they can communicate by reorganizing previously-heard phrases into novel contexts to communicate... which seems like it would require some level of creativity. The fact that you're not using original sounds doesn't mean that you're not communicating something new, after all.
Generally, creativity means the ability to come up with original ideas. But, the Kenku lack of creativity can't actually mean that, because we totally see kenku in the lore producing ideas of their own (like desiring to fly, deciding to seek out ruins that reach to the sky, or applying mimicked sentences or schemes in new contexts). As such the line between what they can and cannot do tends to come off as weirdly arbitrary and vary widely by table.