---- X2 ----Have just about 10000 miles on my 2019 Touring AWD. I have had the "ECO" button turned on for all except two tanks of gas.
I don't need or use "jackrabbit" starts and the car has plenty of power pulling away from traffic lights, stop signs, into highway merging, etc. I have never felt the car was under powered while using Eco mode. One of the biggest differences I have found is the transmission shifts better (no harshness, no jerks, no constant changing between or hunting gears). I have the 9 speed transmission and am very happy with it.
The other difference is while on the highway using cruise. I use the normal mode, not the ACC mode. When the car needs to speed up while using cruise, it takes a bit longer to gain speed because of how the throttle response is managed. It doesn't "floor" the pedal to get back up to speed, but instead gently speeds up. If for some reason I need instant speed, I'll just step on the gas myself.
The two times I did run without the Eco mode on, I really didn't notice much if any of a difference in fuel economy. I will say I did notice an increase in power when starting from a standing stop, but really didn't like it or need it. If I step on the gas leaving a stopped position when the car is in Eco mode, it responses with plenty of power.
Note that I am getting a life time average of almost 23 MPG, with about 80 percent local driving. Very few highway miles the last few months.
My 2019 gets 19-22 mpg in STD drive improves by 2 miles with ECO. I use ECO combined with cruise in long trips. My Acura TLX I4 pushes over 40 mpg with ECO in long trips. If you getting 15 MPG have it checked. I had 2006 Pilot never got less than 19. Yes you lose power in Honda but no power loss in Acura.2019 Canadian Touring...
As well as totally killing the performance so it feels like I am driving a big brick with no acceleration, I actually get WORSE gas mileage in ECON mode than in regular drive mode.
I tested over 2 full tanks of gas 1 week apart to make it fair, and averaged between 13.5 and 14 l/100km over a full tank in regular drive mode, and 15 to 15.5 l/100km in ECON mode, same driving conditions, same timeframe, same type of weather, mix of city stop-and go and 80km/hr arterial 'highway' commuting. Probably because I had to mat the gas pedal anytime I wanted to get moving as it was so sucked out in ECON mode it just didn't want to accelerate.
Test it yourself, you'll probably find the same as @adg8165 and I did.
My suggestion is to ignore that mode, it's pretty much useless and does the opposite of what it's supposed to do.