Really, the degree to which light pollution erases the sky is incomprehensible unless you have really seen a dark sky.

Messier did use a 4 inch refractor, what we would consider a kid's toy today, but telescopes in that day did not help much with brightness and Messier objects tend to be diffuse and dim. Nearly all of them are visible, if only as smudges, with no telescope at all, and the main reason Messier catalogued them is so that they wouldn't confuse comet hunters, who were looking for new dim fuzzy diffuse objects. Resolving any remote galaxy as a structure like a wheel requires either a fairly large aperture, photographic film for time exposures, or preferably both. Those nebulae which turned out to be actual galaxies were not properly understood until the twentieth century when individual stars in the nearer ones could be resolved, revealing them to be "island universes" much like our own Milky Way.

Messier's finds and large aperture tech came somewaht later?

Messier and Mechain had essentially the same technology at their disposal, astrolabes (the real workhorses of astronomers of that period) and modest aperture long focal ratio telescopes. Realistically useful large aperture and short focal ratio (better for light amplification) telescopes did not become practical until the late 19th century. (There were a few earlier examples, but their use was very awkward.) Mechain had basically the same goal as Messier, discovering comets, the same technology, and the same problem of avoiding confusion with existing permanent objects that kind of looked like comets.

The methodology of the day mostly depended on naked eye sky scanning, using an astrolabe to accurately measure the position of a target object in the sky. The small telescope might be used once the object was spotted to see if it could be resolved into something more interesting than a diffuse smudge. (For the most part they couldn't, but the telescope could make a cometary tail visible much earlier than it would be visible to the naked eye. This sort of observation was normally only attempted after the object was located and identified.)

...in a very dark sky. However, you will not be able to resolve it as the "sombrero galaxy" as you see in all the astronomy textbooks. Nobody saw an image like that until photographic film time exposures became the norm in the early 20th century. What you will see is a bit of smudgy faint light, more diffuse than a star, which is always in the same place in the sky with respect to the stars. And that is exactly what early astronomers like Messier and Mechain saw.

Thanks for bringing this here!