Berlin is affordable but that's it. You won't find the best people, the best teams and a good legal framework.
The UK has a better legal system. The UK Ltd. is way superior to the German Ltd. and soon they will move away from the EU inherited laws which are too much market regulating. Especially consumer protection and labour law are just a big bummer for many and for startups in particular.
Besides, just check total fundings, exits, average fundings sizes, etc. then you see the difference. Berlin based startups got much moeny the recent years but slowly people question again the ecosystem since exits are missing. Ok the city doesn't have the startup history like a Valley or London but still. Clear successes are missing. The only huge thing was Zalando's IPO.