The systemic issue with hyper-durable portals and historical key duplication
Over on the Wayfarer forum there's a discussion about a durable portal that I'm pretty sure is not technically a candidate for removal but it (and others like it) break the game in some kinda bad ways. I wrote a fairly long explanation for the PoGo players about how this works and why people wanted that portal gone and added this to the end:
To some extent I believe this is a flaw in the Ingress game design. Strategic and tactical portals have always been a key component of the game for those who play it in that way, but one of the limitations on them was that you had to physically go to the portal to hack keys. This meant that gaining keys to strategic portals required significant effort and thus they were used rarely and with careful planning.
Some years ago Ingress introduced a type of capsule that you could put keys (and other gear) in and items would duplicate. The chance of a duplication was random but was on the order of 1% per day. This allowed people to put high-value strategic keys into capsules and over time make more of them... exponentially more. For example: I was once gifted a souvenir key to a portal in Antarctica, just one. I put it into an interest-bearing capsule and let it cook and ended up with dozens... I gifted a key to a few friends so they could also have a cool souvenir and those people did the same thing and also ended up with dozens.
So imagine you somehow managed to get to the Moloka'i lighthouse and capture it for your team. You would farm as many keys as you possibly could while you were there, but unless you had a lot of time to spend there you could probably get a maximum of 50-100 keys. That's not a lot, and you would use them judiciously. Enter capsules that allow duplication. Assuming I've done the math right and that the interest rate was actually 1% (it was close to that but I'm not sure of the exact number) a year later you would have roughly 1900 keys... which means you could use them quite liberally. Two years later you would have over 71K keys. Even if you started with a more modest ten keys you'd expect ~375 after one year and over 14K after two years. One person can only hold 2000-3100 items, but that's OK... spread the keys out among a couple hundred players and the team still winds up with that many keys only they're geographically distributed for easy sharing and use.
Niantic recently removed the ability to duplicate items but for longstanding high-durability portals the damage is already done and will probably persist through the time that Ingress sunsets.
This combines with Niantic's rule that safe pedestrian access means that someone has to be able to access the portal and you get into situations where it's nearly impossible for anyone to ever access a portal and it becomes a permanent, untouchable asset for one team and that team now has nearly infinite resources to use it as often as they want. I've certainly gone to some extremes to access difficult portals and my teammates have as well. At some point difficult crosses over into impossible (at a practical level, at least) and Niantic doesn't handle this case very well. It's a thorny problem to be sure.
I understand why Niantic removed key duplication, and I'm fully behind them on that decision. Unfortunately that doesn't really help the current problems because of a combination of two factors: the massive number of keys to strategic durable portals that were acquired through duplication, and the fact that some of these portals have effectively become inaccessible over the years. Niantic has always said something to the effect of a portal is considered to have safe pedestrian access if someone can access it, and that it doesn't have to be accessible to everyone. I understand where that rule comes from but the years have really shown why it's problematic.
Imagine a location that, say, ten people in the world are allowed to access. One time, five years ago, they had a special limited tour and someone managed to light up the portal there and farm a couple dozen keys. Since that time the facility has had a budget cutback and now the only people who can get there are two researchers and a caretaker and they're all in the witness protection program so you have no way of figuring out who they are. However, that one agent who farmed a few keys well and truly understood the lessons about compound interest that they got in math class. Now the team has 3000 keys to a portal that no Ingress agent has been able to get to for years.
Is the game any less broken now that those 3000 keys can't turn into 5000? No, I don't think so. Even if the team used one key every day it would still take eight years to exhaust their supply of keys. I'm fairly certain that Niantic's goal was to have a competitive but sometimes-challenging playfield, but not one in which one team can lock up an asset for years and use it with impunity because they will never run out of keys. That's just not a good game mechanic.
What's the solution? I don't know. Maybe Niantic needs a better definition of pedestrian access, one that doesn't permit portals that are technically accessible to a handful of people but in practice are inaccessible... though I don't know how to define that in a workable way. Maybe they need a different game mechanic about long, longstanding links. I don't really have any answers. I hope that @NianticBrian and the team are thinking about this.