When I did up my place, 13 years or so ago, the Worcester rep and technical convinced me to fit a 42Kw combi. Worse thing I did. I had 3 showers but I had one of those as elec for back up reasons. The shower, IIRC, was 10.5Kw, and was, just, okay. 2 years ago, I ripped it all out and went with sealed CH / UV HW. It is like a different world. And 3 proper showers.
Having 2 bathrooms on a combi isn’t the end of the world, necessarily, but why would you recommend something that we all know can be bettered? Agreeing that one designs a heating system based on the individual rather than the house is nonsense. Agreeing with client demands, and fitting accordingly, is fair enough, but it does not make the selection correct.