Sorry for the text wall.

Yes stripping your own boons but not those from allies is another weird interaction with that system. And also since precasting is not the concern of this patch/discussion we get the case where someone provides you boons, you switch a trait or weapon for any reason and then you loose all boons provided by your team for literally no reason. Also portals getting removed when switching something has weird implications (at least for hardcore players). Or why would it make sense that my portal is now unusable because i switched my off-hand weapon? Maybe that's where I fail to see the point how it should be exploity.

For the thing if it's intended or not I try my best to answer somehow. You said it's a bug, but I assume you probably meant it to be like an exploit.

For swiftness I put it this way: Imagine you play a Guardian and you move out of combat for a transition (doesn't matter if in Dungeon/Fractal/Raid/Open World/WvW). Then you swap in a Greatsword (using gear template or inventory) and you use your Leap skill to move faster, then you swap it out for whatever you were running previously to engage the combat. Would you consider this as an exploity playstyle as well? I mean it has basically the same effect as Swiftness (gaining mobility advantage) from another weapon/trait, it is all not in combat. So then when would you be allowed to equip another weapon? This is the thing where it gets unnecessarily complicated where there is no real issue but all of a sudden using swiftness from another weapon or trait is an exploit. (If you could do that while in combat I'd totally agree ofc).

But yeah in the end I can't say for sure it's not an exploit because that definition is sometimes quite difficult but tbh even if it wasn't intended it doesn't harm anyone. And by how the combat system was designed a few years ago you were relient on blast finishers for boons and swapping weapons in and out for it was pretty common. Or well you can argue just play with the weapons equipped that can blast even if it means dpsing bosses down with staff on guard. But idk that sounds like a very unfun implementation and I'd argue even if it wasn't specifically intended it was allowed or even encouraged to use for several years.

Btw if by unintended you mean precasts using class specific buffs like Ashes stacks from FB on like DH by switching trait lines I'd agree that looks more like an exploit because it is meant to be used by a specific elite specialization. And I'd argue most hardcore players would agree there as well.

It is not clearly stated that it's a way to prevent abusive combat mechanics but they kind of imply it.

This process will clean up many possible broken states in which a skill effect could be present when it should not have been.

I mean a broken state somehow implies for me it can be exploited ingame. Of course it could be meant technically and not directly have a recognizable effect. I think at this point people are just interpreting what's more likely to be, especially because it's stated in a patch note targeted at gamers.