Servants don't go against that because they represent "progress built on the feats of the past". Without the giants of the past we'd both be nowhere and get nowhere, and so Servants summoning literally represents the "lending of power from tradition", just in a much more tangible way. At the same time they make a big deal out of even though servants are used like that, they cannot be the ones to decide the future, only the humans of the current era may do that. This comes up time and time again, and is just a huge indicator that Nasu wants you to consider it like you need to make use of what the past has left for you in order to progress, but you need to not let the past dictate the course of future progression.