The defense is already dug in and have supplies in place so movement is not as critical as those on the offense(Ukraine)
And typically, it takes an 3 to 1 advantage on offense to overcome an well placed defense. Having air superiority was a “must have” for the Ukrainians and since they lack it all the armour they have will be wasted as its being dashed against the layered lines of well planned Russian defenses.
Not a fanboy of Russia nor Putin by any means but a student of history.
The supplies can’t be in place forever because supplies are constantly consumed. Currently Ukraine has GMLRS and Excalibur precision artillery and Storm Shadow and SCALP air launched missiles to destroy the supply depots and disrupt the logistics.
There is a campaign that Germany should donate their Taurus air launched long-range missiles and the US the ATACMS ground launched one to make the effort to deny Russian supply more effective.
One of the problems has always been that Western military aid comes late after much hand wringing and when it is late the task has already gotten harder.
Biden is slow, but he is not as bad as Obama, who wouldn’t even allow TOW-2 anti-tank missiles. Trump’s first break from Obama’s policy was that he sent Javelins right away.