[DEV Question] Why is this allowed?

[Miste]

No, that will just cause more of this kind of thing. I've often hurriedly joined in the wrong gearset and changed while I cast buffs. Please don't lock this.

I assume it was an accident (and one a lot of people have made once). If it was on purpose, it's definitely bad behaviour.

You misunderstood, sorry I probably didn't write it properly. I meant that the game would not let you switch to a lower item level weapon than the instance would allow.

Like if you had on a i260 weapon and queued for a duty (avg ilevel 230), went in, then tried to switch to an i110 weapon the game would give an error message like "the item level you are trying to equip is too low for this duty"

But if you tried to equip any weapon say between the ranges of i150-i275 (since those are all level 60 weapons) it would let you change it just fine. IMO i150 is a bit generous for an avg i230 instance but it isn't as big of a problem as someone wearing a level 50 weapon in level 60 content.

[Serilda]

Like if you had on a i260 weapon and queued for a duty (avg ilevel 230), went in, then tried to switch to an i110 weapon the game would give an error message like "the item level you are trying to equip is too low for this duty"

Yes, that would be fine. Though maybe relax it for unsynced runs or something so people could do silly challenges with their friends. Full groups trying to clear shouldn't be full of people farming 2.x light or other silliness.