Great thread.
I've been regularly buying wifi on CX since they launched the A359 in 2016. I think I've used it more than you total, I think less than 50x but definitely more than 20x. But my pattern is far more short haul and definitely less than you long haul. Im certain I've only used wifi on CX longhaul less than 10x.
I think there must be something going on with more people using WiFi now. Or maybe Americans use it more. Or less people use it short haul. Or all of the above.
Speed wise, all else equal the 777 wins vs A350 by a lot. We're all clear on that the 777 has excellent wifi. But I have a positive impression of the A350 wifi, it was actually pretty good when it launched in 2016-2017. I have use it almost all short haul, except for three flights. First was to Paris in 2016, then another Paris, then my last longhaul A350 wifi was early 2018 to YVR. But I remember thinking there was no difference between my first use to Paris and my use to Taipei, Singapore and Bangkok. Good enough, not ground internet obviously but not totally impossible to use like some EK A380 flights, some old SQ flights, JAL sometimes and QR too. Those can be worthless wifi experiences and I never had that on CX.
I think back then, in hindsight maybe nobody was using it. It was rare to get WiFi enabled aircraft in CX then after all. And short haul flights maybe don't have the same value proposition. Because we have so many people here now saying wifi has problems, they can't be crazy!
I have never flown the A350 longhaul to the US. Only 777 (and 747 before that). The 777 wifi is fine as far as I can tell. But now that CX is regularly flying the A350 to the US very regularly, including 2x daily to your destination SFO, maybe it is being tested in a way I'm not familiar with. And now wifi is effectively across the entire CX longhaul fleet, while 2 years ago it was still rare. Probably tons of users concurrently. I remember another post someone saying the ISM told them there is an issue with too many users on the A350 at once.
It's unfortunate if true, because base case the A350 wifi was good. Not great but definitely better than JAL, SQs old wifi and QRs old wifi. It was definitely serviceable. Obviously the 777 wifi is amazing.
I last used wifi last week, on an A35K ex-Tokyo. I have a receipt from Panasonic. It was very good and just as I remember from a few years go. Not as fast as 777 but perfectly fine for web browsing, writing emails, using and editing cloud based documents. Not bad at all.