My guess is it would be similar to what it is today, specifically in that the diverse landscape, including the three Andean mountain ranges that run through it, helped isolate regional Colombian cultures (and in isolation they grew stronger). Meaning we'd have a regional, culturally-diverse landscape, with Muisca, Carib, Wayuu and other peoples spread out through the land.

As for it being mostly monolingual under the imagined circumstance, I can't say, but it's possible Gran Colombia (current-day Colombia, Venezuela, Ecuador, Peru, Panama, etc.) would have naturally formed and, under it, a monolingual pidgin.

We probably would know more about the Aztecs and Maya cultures

None of those peoples come from modern day Colombia.

Aztecs - Mexico Maya - Guatemala and neighbouring countries.

My point is that we have to thank the old Spanish and Portuguese empires for their role in extinguishing South American cultures.

Your point is that you feel queasy about how brutal life was back then and you wanted to throw some shade to feel better about your obviously better moral standards, and in doing so you missed the shot in the map by thousands of miles.

Here's some reading: https://en.wikipedia.org/wiki/Black_Legend

I come from a little place in the Iberian peninsula...

As someone that loves to study history, read old mediaeval documents, I know pretty well what our ancestors did.

As do I, and that's why I understand the whole "generational white guilt" spiel, cause I hear it often. Even an educated person such as yourself will be quick to jump the gun.

I get it, condemning their actions gives you the higher moral ground, you feel like a mensch and somehow detach you from whatever shared responsibility you think you shoulder.

IMHO, we can't judge old-day actions with current-day ethics. The same way we don't generally allow ex post facto law, we should be careful to deliver ex post facto moral judgement. If there's a place for moral relativism, it is probably when comparing different times in history.

That is not to say I excuse everything that was done during the colonial times —there are plenty of recollections of senseless atrocities— but there's definitely a tendency to look at all this in a reductionistic and emotional way that I don't think is fair.

I think the Incas were closer. It could have become a clashing point between both empires.

The same could be applied to Apaches, Comanches, Navajos, etc ...

Me too. It would be cleaner, unpolluted, less bloody, and the native cultures would probably be blossoming and making interesting stuff by combining their knowledge with outside influences. Too bad most of them were exterminated and dispossessed (the galleon being just one instance of that dispossession), and too bad they continue to be institutionally and structurally marginalised, decimated, and dispossessed.

Why?

The spaniards have been better prepared for war and overcame the local population in bloody conquest — this is a historical fact that no one will argue with.

How, from this fact, do people come to an assumption that local population had higher moral values than invading spaniards?

Have you completely no idea what pre-columbian era indian cultures were like? I mean, not today's "New Age" versions that have been adopted for Californian yappies, but actual kingdoms, chiefdoms and empires that resided there several hundred years ago.

In fact, most of the army Hernán Cortés used to overcome the Aztec empire were natives that hated the oppressive power of the aztecs. He managed to exploit these regional feuds, and also internal problems of the Aztec government.

The spaniards alone were a skeleton crew, not enough to conquest anything that big, despite having better technology.