Writing everything in C/C++ has its own host of problems, but it's roughly the name of the game in anything realtime. It's easy enough to think about writing one effect or synth in a slower language, but keep in mind that modern digital audio workstation software is expected to run up to hundreds of plug-ins to produce one block of audio, and that's just not possible without being directly on top of the metal. Even vanilla C/C++ often isn't enough; generally, there's a necessity to drop down into assembler or at the very least use SSE intrinsics.