That just sounds passive aggressive to me. At the end of the day, I think it’s best to say what you mean directly, but still in the nicest way possible instead of trying to beat around the bush.

I’d go with “I think X might work better here - is there a reason you didn’t use it?” - because the answer might just be “oh, I didn’t think of that, cool, I’ll do it that way”. Whereas your question implies that they should have thought of it, which could be perceived as an underhanded insult if they didn’t.