This is really a bug for KDE4 and P5. Since some version of KDE4, when I start with KDE, the indexer always grinds my PC to a halt within minutes, because I have many files. I had finally managed to disable it in KDE4, kept my .kde, installed P5 to test, but then it had re-enabled indexing! I had to restart several times until seeing I had to disable it. Can't indexing (and many other things) be opt-in? Maybe the first time you start KDE, you could choose from several options, like what you're using the computer for (some probably won't need indexing,) and/or more detailed options like whether you want indexing?
FWIW, only a small minority of people experience these performance issues; it's not universal. Every machine I've put Plasma on for example has worked like a champ with baloo. So I think a better solution is to fix the performance issues for folks like you! And in the meantime, turning it off isn't hard (System Settings > Search > uncheck "Enable file search").