Quite the contrary. Ukraine should keep it slow and steady.
If this gets serious, the Russian forces are going to fold up by themselves. Why cost any more men then they need to?
All this talk of the offensive failing? Really, no one should've been expecting anything dramatic this was always going to go slower than everyone expected it's how invasions work most of the time (except when forces collapse like they did in Iraq 2003). Ukraine just needs to keep grinding Russian morale into the dust until there is no choice for them to withdraw to the internal instability at home.
Russia lost this war after they failed to take Kyiv, as I said all along. The victory condition was Moscow's control over Ukraine, when they lost this they doomed themselves to a forever war like America had in Iraq. You can't win something, with no ultimate achievable end goal. The question is how long it takes for the Russians to realize this. It eventually happens in democracies by the public getting fed up and booting out war architects. Dictatorships however, have no such mechanism except what we see is happening now.
