First you need to make fast car, then you should make it reliable.
It's relatively easy to make reliable but slow car, much more difficult to make fast one. When you've got good package - fast car - then you can focus on making it reliable. It's way easier than to make fast car from slow one.
Starting in cold it's often problem with rally cars, so you should prepare for it - by testing it and beeing prepared, at least with spare battery at exit of parc ferme time control.
Usually bigger problem is with starting atmospheric cars rather than turbo ones, as those first have more compression ratio - thus more difficult to turn the engine.

Anyway, this years performance of 208 R5 in ERC is farce... In Valais Abbring had problems with many things.