Ukraine is more stalled than Russia.
Russian advances against Ukraine on open ground, succeed when Russian troops, armor, and artillery plus anti-UKR-drone (electronic warfare), are well led to work in combination.
Ukraine does not have the equivalent of that, yet. Ukraine, in particular, does not (yet) have the troops and armor - in close support of each other - for offense.
Ukraine has a major lack of mobility for its troops along the front and from there in depth, that is prepared to shift and move, upon Russian break-through(s).
All that aside, the proto-socialist strategy of the leftist New World Order - that is the spawn of communist China and communist Russia - magically envisions that its creator (that marxist union - both at home and abroad) - can be replaced by ... a new (narrative) version: because progressives say so.
But that confounds the result of: Russia withdraws to its border AND THEN proceeds to bombard the Donbas and Crimea *for years,* because, if the Moscow Club cannot have what it wants, then nobody else can.
What is missing: Forgiving, kindness, love, truth.
What is abundant: Pride, power, temptation.
Russian troops are not well-led by US and NATO standards due to: the lack of a reliable career NCO corps; a rigid, top-down approach to planning and field operations: and profound inadequacies in weapons and equipment.
In contrast, Ukraine follows the Western combined arms approach that emphasizes training, flexibility, a rapid pace of operations, and the orchestration of different military components in a decisive manner.
On the whole, Ukrainian forces are more mobile due to a Russian lack of sufficient road transport. Russian logistics relies heavily on rail up to about 50 miles from the front, where road transport is meant to take over. This is inadequate to the demands of modern combat.
Your conjecture that Russia could make a tactical withdrawal and then maul Ukraine with long range weapons is all too plausible.