Yeah, the big question is what would have happened if Ukraine would have followed the original plan.
As fars as I know, the conventional wisdom is that Russia's military is primarily equipped and trained to fight wars of attrition along relatively stagnant fronts using massive amounts of artillery to wear down the other side. I suspect the U.S. thought Ukraine would lose this type of war so the strategy was to break through with full force at one point, then outmaneuver the Russians.
However, Ukraine, against all odds, seems to be getting the upper hand in the artillery battles, and may actually grind Russia down.
>>>To the rear of the brutal fighting at the frontlines, Ukraine appears to be making the very best of counter-battery fire to suppress and destroy Russian artillery units.
Though Ukrainian troops continue fighting for breakthroughs in Russian defensive lines, artillery gunners are playing the long game for future artillery supremacy. Counter-battery fire, and especially radars that facilitate it with high accuracy, are playing a big part in this. It has
been reported that many Russian artillery units lack counter-battery radar systems to pinpoint incoming fire, with losses of these prized systems having taken their toll in nearly year and half of fighting. In addition, due to their high-tech nature, Russia is hard-pressed to replace them with new units. . . . Russian accounts of the fighting seem to corroborate a growing Ukrainian artillery advantage in some regard. Former separatist commander Aleksandr Khodakovsky opined that Russian artillery can neither suppress the Ukrainian guns nor compete with their longer range.<<<
https://www.thedrive.com/the-war-zone/ukraine-situation-report-kyivs-growing-counter-battery-advantage
Most of the news reports I've seen miss this aspect of the war.
Also, there have been sporadic (unconfirmed) reports recently to the effect that the cluster munitions being used by Ukraine are very effective.