All the people complaining about the progress aren’t noticing the subtleties. The progression is mostly about their emotions. We have Yakumo becoming more and more smitten with Yamato and seeing him as more of a man and Yamato getting better at accepting the lows as well as the highs.
I might be bias since I like slow burns and this has my 2nd favorite character archetype in a glasses wearing older lady but this is quite a realistic portrayal of how most people catch feelings. It’s a slow process that a lot of times you don’t even realize is happening, much like right here.
So yes the physical progression is slow, but we’re seeing them fall deeper and deeper into the others heart every chapter. Which in my opinion means a lot more than if they were getting more physical or if everything was surface level.