the next generation always surpasses the previous one
In
morals. Oonoki pointed that out.
Think about it, biologically speaking, genes weaken by generation, just look at Tsunade in comparison to her grandfather or even her great uncle. If it meant in power, most shinobi would be at least Tobirama level by now, and the exceptional could roflstomp Hashirama, but this isn't the case.
Of course, I noted that in every generation, there are exceptions like The Senju Brothers, the Sannin and Naruto/Sasuke. Further evidence to support this was emphasised when the Alliance cowered upon seeing Hashirama and Madara fighting, noting "Is this how our ancestors used to fight?!"