There seems to be two things everyone is getting up in arms about. The specific issue with Apple slowing iPhone 6's when the batteries started to get older and not last as long. The SUPPOSED reason Apple gave was that they were trying to make sure the battery lasted as long by slowing down the phone. This wasn't "only a year old" and was tied directly to battery health. Then it lowered performance.
The second issue people are talking about is Apple intentionally slowing down EVERYTHING to force you to upgrade to a new device. This "planned" thing is where they do things to make stuff feel old and slow and then you go out and buy a replacement, not because you would "need" to but because Apple has done something to make it appear that way.
Apple did a really poor job in communicating what they did. That is just fact. If that is why people are suing and that is what people want to get paid on, so be it. I, along with a lot of others, feel like the lawyers win instead of the users. But to each their own. It was a mistake and if the court rules in favor of it, there ya go. Feel like this is fairly straight forward.
I don't have any idea if waterproofing is A reason why Apple doesn't allow for replaceable batteries. No knowledge on the subject. However, just because a completely different product, such as an Olympus digital camera CAN be waterproofed, says nothing about a smartphone from Apple. Truly not even something that is a reasonable comparison. Again, no idea if it is a reasonable argument to begin with, but comparing it to a different product category entirely to say it can be done is not very corollary.
I mean whether it WAS or WASN'T honest is pure speculation. I think depending on your perspective each way has merit and a case to be argued. However, I can certainly agree that they did a horrible job on communicating the "feature".
I have been using computers since my first Tandy 8088. My opinion about your opinion is that you are having a very narrow focus and a very strong and emotional interpretation. Computers get slow and old no matter what. It has been that way since I have been using them anyway. The pace of this slow down have a LOT of factors. I understand you think this is a master scheme by Apple to make you upgrade. While I don't quite share the same perspective and haven't had the experience you describe, I feel like you are not helping your point by not acknowledging the general natural slow down and myriad of reasons why this happens. It feels a little "conspiracy theory" like as you posted it.
It's a great question, what is a "reasonable" timeline?
To wrap up my post.....two things though....
Not telling people if you are going to throttle their devices is not planned obsolescence, its bad communication. That is a separate topic. Just wanted to get that out of the way.
But IF Apple is doing "planned obsolescence", that is not the "natural" cycle, that is a forced thing. So the real question is whether Apple is just doing the same thing that computer and software MFG's have done for decades or if they are doing something nefarious to try and raise sales. If the courts are looking into that, then great! (as long as there is evidence). If this is still around a bad communication choice by Apple and now everyone is trying to throw terms at it to make it sound terrible, then it is a waste of effort.