> For example If I remember the debate about Telegram where a highly talented team starts their own library the response from programmers is that they shouldn't do this and instead use crappy old libraries which do not even fulfill their requirements.

The problem with Telegram wasn't about code, it was about algorithms and design. They designed their own crypto, which is a really bad thing. If they had written their own implementations of well-known, tested and proven crypto primitives/algorithms, everything would have been fine (well, mostly; you can still implement a good algorithm badly, but that's not what happened).