I definitely think that would be a generalization, but that's not really what I was saying. Manufacturer's specifications and subwoofer matching tools can be helpful in providing some general guidance. But, it's really the speaker's placement in a room, and it's interaction with the room at that location, that determines the speaker's low-frequency response.
So, I'm not really making a generalization about 6.5" woofers at all, although I did read a review of the OP's speakers before replying. But, I am specifically reacting to the fact that his Yamaha measured the frequency response of those speakers and assigned a 70Hz crossover. Ideally, I would want to go up about a half octave from that initial setting, because YPAO is measuring where the speakers are rolling-off by 3db and setting the next crossover up from that. If they are already down in volume by 3db at ~60 or 65Hz, then I would like to give them some more headroom. 90Hz is as low as I would personally go in that case.
Your own situation is a completely different one. In your case, your measured in-room response puts your speakers a little under 40Hz--perhaps at about 35-38Hz. The FR is just low enough that your AVR used a Large setting rather than a 40Hz crossover. So, when you set them to 80Hz, you actually gave yourself a full octave of additional headroom, which was a very good idea. (Each doubling of a frequency constitutes an octave.) FWIW, I think that speakers which have frequency responses higher up in the 60-80Hz range need less protection than speakers which measure in the 30-50Hz range.
What I mean by that is that a speaker that has a measured in-room roll-off point (F3) of about 35Hz or 40Hz, is going to benefit much more from an 80Hz or higher crossover (a full octave) than a speaker which measures 60Hz is going to benefit from a 120Hz crossover. That's because frequencies below about 60Hz to 80Hz put much
more strain on the woofers in our speakers, especially as we increase our master volume, than the frequencies above 80Hz do. And, of course, our subwoofers are nearly always going to handle <80Hz frequencies better than our speakers will, anyway.
So, it's hard to come up with a single hard-and-fast rule, and I typically try to make crossover recommendations on a case-by-case basis, depending on the actual in-room response of a speaker. But, when in doubt, I would suggest that erring on the side of caution is a good idea. In your case, you have already done that. In the OP's case, I thought that just a little bit more caution was advisable.