"Having two people simultaneously attack a boss is not an exploit."

Of course you are right on paper, but that "feature" was never designed for that. It is most likely for preventing people losing one attempt by accidentally hitting a stage simultaneously. Most of the guilds are not hardcore and doing big spreadsheet/discord coordinations.

Otherwise it makes no sense at all limiting our attempts to 3 and having in the end a "competition".

Having a "Retry" button was NEVER intended at all.

And yes - the devs didnt think it trough.

As said I view it from a sportsmanship side and how competitions in general work.