Putin is using his tanks, especially his older tanks, as self propelled artillery.

I think you mean "mobile artillery". They also can fire SPA, and probably would use that if they are far away from the lines (longer range). They would have fewer of those than "dumb" rounds, I would expect (unless they've already burned through their dumb rounds).

Yes, they are mobile artillery, and also used for infantry support on occasion (along with BMPs...the equivalent of our Bradleys). There is risk with infantry support, due to drones. But there is also risk to infantry from drones (e.g. explosive packages, remote targeting of artillery). Ukraine has used their western tanks with great effect, but they also now are in danger of drone attacks (and, previously, to air attack before the Ukrainians started shooting everything down that came close to the front lines).

Which is why they are picking their boneyards clean...it's difficult to advance without tanks, and tanks attract drones. Trench warfare (which much of the front has devolved into) is a recipe for not gaining much ground, but incurring lots of casualties.