He really wasn't. Very marginal figure, except that in the 19th century his character and role were vastly exaggerated. Compared to Matteo Ricci or William of Rubruck, we don't even have evidence of anything he said. Marco Polo is way too mythologized, and this wonder only plays to that mythologization.
But he was part of the medieval Silk Road, no matter how small. The wonder as I conceive it will represent the cultural, scientific and commercial aspect of the Silk Road, whilst the actual silk is represented by the Damascus and Constantinople terminus.
I agree that Marco Polo isn't the most important traveller of the time, but ultimately he is the most well recognised, and a valid figurehead for a wonder which would otherwise be very generic. Absinthe has said he wants the wonder to stay, so might as well have it something people will recognise.
It's not like there isn't precedent for that anyway. Krak de Chevaliers was no larger or more important than Vadum Jacob or Magrat at the time, but it is a wonder because it survived to the present day. Why is it Magellan's Voyage instead of Columbus or Cabot or one of the many others who preceded him? Copernicus' Observatory but nothing for Kepler, Brahe, Galileo or Newton? All the decisions around many wonders are fairly arbitrary, with the focus more on gameplay than actual historical fact.
On that note, can we just copy and paste Sword of Islam's Eastern Mediterranean/Middle East into the game? The map for England or Scandinavia is beautiful, but the Middle East looks really ugly. Makes more sense to just copy paste IMO. The reason I bring this up, is because SOI has silk resources next to Constantinople.
Don't agree with just copying it in tbh, There are some parts where the SOI map is better, like the Cilician Gates and Sinope being properly positioned on the isthmus, but also some inaccuracies (Jerusalem being level with Gaza, the Mount Lebanon range being right on the coast for example). This has obviously been done to fit as many viable cities and civs into the Levant as possible, but RFCE shouldn't be bound by the same.