Grind is more important then tamp, a heavy tamp can make up for a slightly too coarse grind - but getting the grind spot on gives you the perfect extraction time - I am for 25 seconds on a 10g single shot 1floz liquid but adjust to preference.
But every origin or blend will need grind adjustment - and get this even your room humidity can affect extraction - I learned this many moons ago doing exhibition stands brewing coffee - the grind in the morning had to be finer - as the show filled up and it go more humid during the day I had to make the grind coarser to compensate.
But it's all part of the process - when you crack that perfect shot and go Yum, it's solid gold.