I'll counter with a few points.
Turn progression does not confirm the 300 mm as initially succesfull. We prevented Naval Canallan invasions before the introduction of the 300 mm artillery. Attributing the victory to artillery is a mistake. The turn states :
By the time Cannala hits the shore, some of their Walrus landers have been torpedoed and a portion of their Victoria Battlecruisers have been lost. They are capable of shore bombardment within a good distance of the coast (when men on the ground can provide accurate coordinates) but eventually the Forenians, who still have an advantage in infantry combat and benefit from their now-cheaper Salamander, drive Cannalan forces back
It was a combination of air, vehicles, infantry and the 300 mm that did it. Attributing the victory entirely too the 300mm, as you insist on doing, is highly misleading.
It's better to look to what is actually said in the turn reports :
A portion of the Victorias were destroyed. Not all of them, not even the majority. A portion. Meanwhile, our entire coastal artillery in the relevant section was lost. So, it's my assertion that our artillery is inferior, but our pre-existing advantage + cheaper Salamander overcame that weakness.
Though I was wrong about the Spearhead being referenced as a better interceptor, the fact remains that they're not going to be shooting down our bombers if they've been shot down themselves -- air superiority matters, and when it comes to deciding air superiority the Thunderbird shoots the Spearhead down better than vice versa, making it superior to the Spearhead plane-to-plane
That's a value judgement, and one I consider incorrect. Our 300mm cannon bunkers got bombed because we couldn't stop the enemy bombers, while the enemy did not need to worry about our bombers because they got intercepted and destroyed. It is a lot harder to destroy all interceptors than it is to stop a meaningfull amount of bombers.
The problem had been complexity, which they didn't have because they had done engine work the previous turn on the Bull.
Remember, we did 2 engine revisions. One for power, one for complexity. If it were 1 and 1, it would've been fair.
Besides, those engine issues are still troubling us. Despite rolling a 6 our bomber still got weak engines. Oh, and our revisiin made our engines more expensive.
Expensive Tbirds coming off of Very Expensive Zheleznogorods, and Expensive Spearheads coming off of now-Expensive Santos.
Z-class is 50% larger, so that should not be an issue. We should still have numerical parity in jets.
The problem is noted in the turn :
Despite the fact that Forenian aircraft and torpedoes are still very effective at doing their jobs, too many of them get shot down by Cannalan aircraft to eliminate Cannalan fleets by themselves
The enemies interceptor jet intercepts our bombers. Our fighters superior dogfighting ability can not safeguard our bombers, because it can't shoot down 100% of all planes.