I have personally found two different sorts of big babies. Those who eat constantly and those who, because of their size, are often able to sleep through the night early in life.
My little guy was about 12 pounds at 4 weeks... I can't find his records right now but he's a big boy (both he and his sister were/are in 95-99%). So is his cousin who is literally off the percentile charts (wearing size 2T at the wee age of 10 months). Both were breastfed babies, mine to the age of 3 months, cousin to the age of 6 months.
My guy doesn't eat at night anymore, just started that at 3 months. We are having troubles with his sleep right now and it has been suggested maybe he wasn't ready to give up his night feed even though he is eating enough during the daytime hours and will fall back asleep with the paci prop. His 10 month old cousin, on the flip side, is still getting up at 1 a.m. and 5 a.m. to eat a full bottle.
I am no EASY expert here but it surprised me to see you are already on the 3.5 EASY at 6 wks. I wonder if feeding him more often during the day might help. Or, have you tried cluster feeds at night? Or, have you tried the dream feed?
My other gut reaction here is that it is normal to still be feeding at night, especially a breastfed baby who burns the calories faster than he would formula. I see your wanting/needing to tweak the EASY to start eliminate feeds though, thats about the time other babies start SSTN and its hard when yours isn't yet.
I hope you get some good advice from the experts here, they're great! Best of luck and HUGE hugs on the sleep deprivation -- totally understand how hard it is.