Actually dilute the acid is stronger, concentrated sulfuric acid can passivate metals like iron or copper.
concentrated sulfuric can be used in iron vessels because the iron passivates but if we added water we would dissolve the iron pot.
Look at the concentrated sulfuric acid cell used to remove gold plate from copper we passivate the copper (here we can actually use a copper screen wire as an anode basket, were normally the electrolysis of the anode will force a reaction to occur that normally will not (or dissolve a metal into an acid that would not dissolve into the acid without it being the anode), but if we dilute the concentrated H2SO4 acid we can easily put copper into solution or dissolve our copper anode basket...
Nitric can also passivate metals when concentrated, take silver for example, concentrated nitric has much less reaction to attack silver, (at least in the beginning until we form NOx gases in solution), but a more dilute nitric will readily attack the silver and actually dissolve more silver into solution than the concentrated nitric acid will.
concentrated nitric can be stored in aluminum, (or stainless steel), where the dilute acid would attack the metal.