Interesting and overall positive developments.
1) I was wrong in respect to my assessment of Plako's rationality. As it turned out, he had a sufficient force to cover his northern city. After that, he burnt two border cities we had but has wisely chosen not to proceed further.
2) For a couple turns after that we were just staring at each other doing nothing. Plako's positioning indicated that he does not want to press his offensive further.
3) Today I logged in to see a peace proposal from Plako. I accepted as I am not going to have resources to damage Plako in the next ten turns anyway. It turned out to be a very smart thing to do because Commodore DOWed on me. He brought 11 Praets and some Trebs.
I am totally not surprised. The best strategy for Commodore would be to wait out until me and Plako damage each other and then join in on the side of the victor. Also, our current geography makes it extremely difficult for any of us to gain something from war: we have only one couple of neighboring cities and they are five tiles from each other. But, as I have stated very early in this thread, Commodore is a lunatic, he just does random stuff.
I offered peace to Commodore. He has to accept as I am no longer at war with Plako and have higher power. But he is a randomer, as I have said, so it's a 50/50 chance.
4) Hopefully, we end up here with a stable three powers dynamics where no one is able to attack any of others because of the risk of a dogpile. It is sad that it is taking so much trial and error for my two neighbors to realize this.
5) It looks like Plako will get his stupid city after all: he has a settler ready and we are at peace. Well played
I am not sure, however, whether this city was worth it and it definitely makes a probability of a conflict between us in future much higher. It is not even a good city at this point, because it is going to be crashed by my culture: I am fully prepared for a culture war now. Don't know why Plako wants it so much.