I did a Veloviewer search for rides on similar days… endurance rides are at similar power and similar routes.
Checkpoint road/gravel bike with 48mm (measured) S-Works Pathfinders. Definitely not a road tire.
Tarmac SL7 road bike with 33mm (measured) GP5000 All Season TR tires.
Ok, almost no wind.
2mph WNW wind 
riding west 
into headwind: Checkpoint
2.6mph WSW 
riding west : into headwind: Tarmac
ok road surface:
Checkpoint using Garmin RS200 power pedals, Tarmac has SRAM/Quarq Red crank. Last time I had RS200s on Tarmac and dual recorded they were pretty closet to each other: Garmin Rally Power Meter Pedals: Look Road, Shimano Road & MTB - #448 by WindWarrior
Later in that ride
2mph WNW wind riding North 
into headwind: Checkpoint
2.6mph WSW riding North with slight tailwind: Tarmac
poor road surface:
Well that is a head scratcher. Usual erg-like power, just like the previous westbound segment above.
Didn’t control for body position, however I’m usually practicing the same alternating good/better aero position during endurance rides.
Biggest difference was Checkpoint ride I was testing out a new & properly tight fitting vest, worn over a new long sleeve spring/fall jersey. And new bibs (summer).
The Tarmac ride was my usual bib tights and long sleeve fall/spring jersey.
Anyways, in that truly non-scientific test, without boring you with more data, here is the clear winner:
fenders 
and 48mm gravel tires at 50psi. I’m gonna bro-science it and give credit to the fenders and that vest.
FWIW, I have NO trouble keeping up on 18-22mph group rides on that bike.