I've provided a fair bit of evidence, based on player trends and the overall state of the game, that strongly indicates that the Arc has had an impact on the game that's wholly unmatched by any other GB. Alcatraz and Chateau come close only in terms of the base bonus, as they're both powerful effects as well. However, Alcatraz only gains 1 extra unit per level rather than 5 and Chateau's bonus goes up 5% rather than 50%, which is about what they'd have to be in order to match the Arc's impact. You're just not choosing to accept the evidence I'm providing, that's all.
Opinion ≠ Evidence
You haven't provided any "evidence" that the Arc is overpowered. You've only stated why you believe it to be true based on your own interpretation of the situation. This is what is referred to as "opinion". Opinions do not serve as evidence.
It turned into an exploit because players intentionally sold the GB and rebuilt it in order to continually reap the rewards. In the simplest terms, exploiting is taking advantage of something or someone. When it comes to gaming, that usually means something that's unintentionally (usually by oversight) designed in a way that's more beneficial to players than it should be. Getting rewards from a GB, correct, that's the design of the game. The Oracle giving the rewards it did was an oversight, and the player's reaction to it was exploitive. Pretty cut and dry here, and that's ultimately what led to what happened. If so many players didn't take advantage (read: exploit) the Oracle's initial design, this thread would not exist.
If no one had complained, nothing would have been done. It would have been awful for the game, but if NO ONE had complained... then it would not be considered abuse and it was wholly within the rules to do what was done. Maybe the developers decide on their own to change it down the line if they feel it isn't what they intended. But until that point, it would not have been an exploit. Just bad design. An exploit implies doing something that was never intended. Using an Arc to boost bonuses... intended. Collecting prints to construct GBs... intended. Ability to delete a GB once built... intended. Semantics at best.
One does not blame the player for using a system, staying 100% within the rules, of abuse simply because a developer fails to properly test something. "Staying 100% within the rules" is the key to my perspective. It was not against the rules to do anything that was done. The developers released an imperfect GB and the players used it as it was. That is not abuse. There isn't anything in the rules that would tell a player... don't go after something if you "think" the reward is too high... just tell us the reward is too high and we'll lower it. Maybe it is incumbent on players to simply "realize" that this isn't what is intended and use some simple "game ethics" -- that's fair. I just don't like the word exploit in this case. Perhaps that's simply a "me thing".
Now... a bunch of players recognized that this was probably unintended and the adjustment was made. Fine. I'm not mad at that. What I am mad at is that they chose to hurt ALL of the Oracle owners in doing so when there were in fact TWO methods to apply this "fix". They chose the method that would impact ALL players instead of just the ones who could take advantage of the issue at hand. And then, rather than bothering to research the impact of their mistake, they again haphazardly applied a "fix" which was wholly unnecessary. Those are my issues with what has happened.
I think the takeaway here is that your definitions of 'exploit' and 'overpowered' differ from my own, perhaps. What constitutes these things to you?
Clearly. I've already explained why this was not an exploit based on my particular "definition" within this context. Overpowered: I don't think this is something that can be defined to a specific point in this context because it can be for a variety of reasons. However, you are correct... I do not define overpowered in the way you do if your definition includes the Arc (or Rogues, for another example).