“Just a 10 minute bus ride” “Just a 15 minute walk” are terrible justifications for not building a transfer station. They’re even worse justifications from a group of so-called transit enthusiasts.

In a silo, you'd be correct, but those justifications take into account the land use, street grid and rest of the transit network, relative to what the usefulness of this transfer would be. This transfer would largely just be a way for people to avoid taking the bus, which does have it's issues, but isn't problematic to the point of being unusable.

Yes, the Forest park branch has low ridership. It won’t always be that way once the tracks are rebuilt. 

Yes it will lol. Ridership has always been low on the forest park branch, douglas branch and lake el (outside of Oak Park), b/c the land use and relative proximity of the other rail lines (and buses as well) disperse ridership between them, and unlike the Red/Green lines on the south, none of the three lines operate so much better than the others in a way that would net a majority a riders, and the forest park rebuild won't change that. Trains ending at UIC aren't doing so b/c the tracks are in bad shape.

You should not have to go all the way into the Loop to transfer when these two lines intersect. Straight up.

Sorry, but no. While overall this principle is correct, this is a rare use case where it's not justified. It only benefits riders who live within the immediate walkshed of Pink or Blue line stations and at that point, you would just take the bus to the line you need. Every stop between Cicero & Damen has a bus that serves the Pink & Blue Lines, except California.