So long as you are willing to vary between the London System and Queen's Gambit as white, you should be fine.
Chess players, when they say the London System is not good for chess development, are directing their comments to those players who only want to play the London system as white.
Hey guys,
I am 16 years old and I come from Germany. I have play chess for one year. My DWZ is 1086. In every chess game in torunaments, I played the Queensgambit. But I would like to play another opening, too. The London System! I am a solid player. I will never play kings gambit or other openings, which are very sharp and riskful. So I asked a good chess trainer in Germany (2400 Elo), if the London System is good for my chess development. He answered: Yes, of course. There are a lot of other chess players, who play this System. But in many german forums i read, that this System is not good for the development. If you play this System, you will not be better. Is it right?