2S19 MSTA-S 152mm

The MiG-1 back then wasn't considered to be terribly useful. It was basically designed as a high altitude interceptor and most combat took place at lower altitudes in the Eastern Front. For much the same reason as the Soviets didn't like the Spitfire, they didn't like the MiG-1 or MiG-3.

The western view of the MiG-1 and MiG-3 is coloured by the view the Germans had of such aircraft at the time.

It was only later when they worked out why they were losing high altitude recon planes over Soviet territory that they realised the MiG-1 was doing its job just fine.

I would not compare the MiGs with the Spitfire, the Spitfire was more like the Yak family of fighters, the MiGs were more like the Hurricanes... not as advanced but a bit more solid. But they wanted more Yaks than more MiGs... which changed when the MiG-15 was put into service.

The Yak-1 was a decent aircraft, but it entered production kind of late, so it wasn't available in large numbers when the war started. It also required a whole new production process.

It was a bit more work to make than the older cheaper simple Polikarpovs but they were never going to make subsequent aircraft designs at the rate they made previous models. The Yak-1 was accepted into service in 1940.

Perhaps the V-12 engines that the Soviets had back then weren't good enough to make it a decent fighter

Ironically it was the lack of really powerful engines that led to them making their fighters lighter and smaller and shifting to cannon armament faster.

A new caliber gun also means new firing tables, which means retraining artillerists. The Koalitsiya has a robot do all the cool things between the gunner selecting the ammunition and pressing fire so its there's no issue at all with changing calibers.

Plus as the older barrels wear out and need to be replaced and the money is available (ie is not being spent on more urgent things) they can give it a new longer barrel and an electronic upgrade that will make the range tables obsolete because it will be all automated like it is with Coalition.