Flow does not always equal filtration. Power heads can give lots of flow with 0 filtration. Eheim canister filters give lots of filtration with low flow.
Your fish will not die from having too much filtration as long as there is not too much water flow. You can, however, waste money on unnecessary redundant filtration. Your bio load will only support a certain amount of beneficial bacteria. Once you have enough filtration to house that bacteria, extra bio filtration is wasted. Your fish only produce so much poop. Once you have enough flow to capture that poop (mechanical filtration), any extra mechanical filtration is wasted.