Be careful reading tyre load limits...remember you have two tyres on your bike, and maybe something like a 30:70 weight split f:r, so the highest static load on the rear wheel and could be estimated as 0.7*120=85kg, this is roughly the actual load on the tyre.
Schwalbe website does stat "Maximum load" for their tyres:
https://www.schwalbe.com/en/tour-reader/marathon-supreme.html, 700c versions of Marathon Supreme seem to vary from 85kg to 110kg with increasing casing width.
Roadies seem to be all about "bigger is better" at the moment, largely fuelled by Jan Heine's research/reporting and all these endurance/adventure/gravel/bikepacking bikes. After ~15,000km on various 700x40c tyres on my gravel bike I'd say I have no problems with that extra girth over a road tyre, and the extra grip and comfort is much more valuable than a few hundred grams in mass.
All that said, I'd say for a one off use any slick 700x28 to 40ish tyre should work a treat, but there's also heaps of really nice 700x40ish to 29x2.0 slick or lightly treaded options now which are heaps capable on and off road!