I was a tank commander on an M1A1, as well as a transition instructor for different versions of the tank.
The M1A1 is more than capable of being an effective contemporary MBT. The main differences between the A1 and A2 are an independent viewer for the commander, touchscreen interfaces, and the tweaking of certain minor issues, like a larger bustle rack. The basic performance parameters of firepower, mobility, and armor protection are essentially the same for both versions.
On the A2 the commander's independent thermal viewer (CITV) gives the tank a real advantage in long range multiple target environments like the open deserts of the Middle East. It doesn't give you much of an advantage in urban or heavily forested areas.
All Abrams variants are complex machines that require significant training to employ safely and effectively. Setting aside my opinion on whether we should send tanks or not, the A1 version requires less training time than the A2, and the A2's upgrades would not provide much of an advantage in Ukraine, so it's a logical choice given the combat needs and urgency of the current situation.
And these aren't tanks that have been in a boneyard for a decade, they are newly rebuilt/refurbished machines.