No, Queen is at worst mid diffing their strongest member
In 1v1 I doubt it's even a high or even mid diff battle. And that's not all the F6 who want to challenge Queen, it's Sasaki and Who Who. Even if they manage to band together I don't think they have a chance to beat Queen.
-Based on the details the Flying six(at least Sasaki/Who´s Who) should know about Queen and the calamity power overall very well, yet they are very sure to having the strenght to became a Calamity.
-King use Kaido name to call them out because otherwise Sasaki and Who´s Who couldn´t listen him
-King hyping them up and even give them the promote to get the chance to became a calamity if they find Kaidos son and bring him back.
-Again Sasaki and Who´s Who get the hype by Oda
If the gap would be large as you guys make it sound like(Mid diff) neither Oda or King would hype them up so much, alone by portrayal it doesn´t would make anysense.
@Sade
We don´t know when the Flying six get create, but the only fact probably is that they aren´t be one of Kaido crew back then when we see the clash between Oden vs Kaido. Another point is that I don´t think anyone of them or at least Sasaki/Who´s Who going a mid diff material for any Calamity while we having King himself hyping them up after Oda already did in the last chapter.
I agree the Calamity are still most like stronger, but a mid diff after all the hype they get? I doubt it very much, as I said I wouldn´t be surprise if Sasaki and Who´s Who having a bounty about 700-900mio.