Russia does have reliable self-propelled tube artillery - but even the US has found that our SPGs are unable to keep up with the Abrams over the course of the last several decades. Russian rocket artillery is more developed than ours, more diverse (as in types, not the Biden sense), and *can* keep up with the armor. In fact, nobody’s been able to come up with SPGs that can reliably keep up with the armor, even in exercises unless they’re unrealistic.
Something worth noting is that while both sides have evolved versions of armor and artillery that was in use in the Soviet period (Ukraine was the armor/vehicle development and production area of the old USSR), the Ukraine generally has merely reasonably upgraded versions of the kind many people here think would be easily defeated by US weapons and the Russians have (not uniformly, but in sufficient numbers) hugely upgraded versions, plus new vehicle/weapon types that were developed after the separation. The latter is what too many people here stuck in the 80s and 90s are denying exist and are likely why this is looking like a walkover.
If the Russians try to do to Kiev what they did in Grozny, then already bogged down they will invite NATO airstrikes invited by Ukraine.