Well, you are right that the programs of SPD, Greens and Left are pretty compatible with each other, but the statements were made. Maybe that is to avoid fear-mongering (which is happening anyway), but it seems that there is some substance. Also I doubt the Left will easily let go of their pacifist foreign policies, as this would split the party and make them even more irrelevant. But you are right again, that the Left is pretty weak at the moment.
Greens have shown in the past on provincial level, that they are quick to abandon their ecological agenda for a coalition with the CDU, leaving only some token policies to look like they keep their promises. So despite their strong language regarding climate agenda, I can totally see them give in to be part of a coalition. For the SPD we already know this for a long time, that they give up whatever agenda they have, to be part of a coalition. This lead to SPD voting against their own proposed laws, because they were brought to vote by the opposition and SPD voting for a law only to vote against it a few months later (there was an election in between, and SPD was going from government to opposition).
So overall i think red-green-red is quite unlikely, between the distancing statements and the overall weakness of the Left. It will not be enough for red-green, I highly doubt it (but if there are just enough seats, I actually see that as the most likely coalition). If red-green has not enough seats, then I see them going for CDU or FDP.
A reelection is highly unlikely, as the big parties all probably will lose even more votes. Before that happens, I see CDU voting for a SPD-Green minority government. That would actually put the CDU in a comfortable position to oppose everything while red-green isn't able to get anything substantial done.
As far as I know, neither the SPD nor Greens have made explicit statements against a coalition with the Left. Instead they merely opted against endorsement of such a coalition which is not the same as ruling it out. From the side of the Left, in their paper for possible coalition talks after the election they have not included their usual call for Germany to leave the NATO, so that's kind of the same thing going on. All three parties are remaining purposefully vague because they all know of the paranoia and don't want to lose votes on the final stretch of the election campaigns.
If you've watched any of the three-way discussions on TV in recent weeks, it has been pretty obvious that SPD and Greens see it as a high priority to keep the CDU/CSU out of government. Scholz and Baerbock repeatedly teamed up against Laschet despite not agreeing on everything with each other. That's why I see neither the SPD or Greens pursuing a coalition with the CDU/CSU, so all other possible options will be evaluated first, the obvious exception being the AfD which nobody likes.
Right now, red-green-red has about 50% of the current polling, so that's a majority after the insignificant parties get removed from the equation. In case that the Left fails to meet the 5% threshold, we'd be looking at ~10% of the total amount of votes getting discarded, meaning that SPD and Greens would need only ~45% of all votes to hold a majority of seats. If the Left falls below the threshold of 5%, it's likely that those votes would be lost to the SPD and that would result in ~45% for SPD and Greens combined.
As for parties abandoning parts of their agendas in coalitions, that's the necessary compromise to get something done instead of nothing. How much a party can get through in a coalition strongly depends on their share of votes in the election. The only Bundesland where you can really criticize the Greens is Baden-Württemberg, because it's the only one where they lead the coalition and could definitely get more done than they do. The reason why you see less bending from the CDU in coalitions is because in almost all of them they are the leading party.