not always, the timing could be out and you never noticed! sounds daft but i drove a phs1 172 with cira 150bhp at fly (didn't know this at the time and that's coming from me "mr expert" alledgely
) granted i proceeded to overtake a gallardo superleggera round the outside, in the wet at oulton park LOL turned out the CAT had collapsed!
but as you say they maybe bob on, this is the problem! Luck plays its hand a bit, but to be "safe" go to someone with a good reputation who backs up the work they do without quibble - safest option!