My thoughts are that you haven't seen much of Raphinha or Coman if you believe they would be an adequate replacement for the second-highest City goalscorer of the 21st Century.
For every successful Bundesliga import we see (Sané, Aubameyang, Gundogan and even the first two were only for a few years) there are countless who look amazing in Germany, come here and we quickly discover they're not up to it against PL defenders (Haller, Kagawa, Mkhitaryan, Sancho, Joelinton, Werner, arguably Havertz etc.)
Sterling is a proven Premier League goalscorer, one of the best of the last decade, and it's staggering how much we undervalue that as a fanbase.