I'll chime in one last time.
1. Apple should honor their service offering, or at the very least provide succinct requirements.*
2. Batteries degrade, however, you can't judge battery performance strictly on the battery itself. For example, software problems can cause constant processing, additional/unknown background tasks, and usage e.g. you may think Web browsing is low taxing, but in many cases it's very much not, including but not limited to media, page styling, advertising display/trackers and other scripts.
3. Don't obsess over the battery "health" percentage -- this should go for Apple support personal as well.
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I have very strong doubt this battery is at nearly 86% of its original capacity. Even if somehow so, the full charge cycle count and age far more accurately imply the "real" performance: frequent OS UI and app crashes and much slower performance than this device had originally i.e. CPU/GPU throttling. I haven't replaced the battery, nor do I intend, therefore, any conclusion to these issues being related solely/primarily to the battery degradation is indeed still speculation, not a fact i.e. verifiable.
Ultimately, don't get caught up in the placebo effect i.e. exaggeration, and when a problem does arise, go through proper diagnosis/troubleshooting.
* Too bad an Apple Genius Bar employee can't chime in on the specific guidelines and perhaps why they're in place -- assuming they might be privy to that knowledge.