Isn't the current generation of iPhones internally limited to 7w wireless charging? Your results seem consistent with normal charging pads, which take about 4 hours to fully charge an empty Xs Max.
I can't really say, as I don't usually monitor the time to charge. I either just top it off wirelessly all the time, or I pop it onto the Qi charger at bedtime and when I wake up 8 hours later it's full.
I just wanted to report on the performance of the portable Qi charging battery pack that I had just recommended. To summarize:
My Xs Max went from 20% to 45% in 30 minutes (25% added in 30 minutes)
Then up to 50% charge after 40 minutes
Then up to 55% charge after 50 minutes
Then up to 60% after 60 minutes (40% added in 60 minutes)
Then up to 70% after 1 hr 15 min at which point the charge rate slows a bit
Then up to 86% after 2 hr 10 min
Then up to 90% after 2 hr 30 min
Then up to 95% after 2 hr 45 min
And hit 100% after 3 hr 10 min
So yeah, it's possible that it could take 4 hours to go from 0-100% on the battery pack.
But It seemed to me that for the first 30-60 minutes that it was charging a bit faster than a 5W USB cube, and maybe as fast as a 10W cube, before it noticeably slowed after an hour and 15 minutes (after increasing the charge level by 50%).
After that it seemed like it was charging like a 5W cube, but adding 50% to my charge in an hour and 15 minutes on a wireless battery pack seemed impressive to me.