I only see your arguments as acceptance and excuses.
I have had titanium tubes made at the same plant these gun tubes came from. We got ours much cheaper than gun tubes.
were they the same alloy ? and were they processed the same way ?
Your argument is basically with people like Tom Eagar who says total cost of a physical structure is proportional. (~x10) to the raw material cost.
https://nap.nationalacademies.org/read/10631/chapter/13
And that has proved true from hot rolled in commercial shipbuilding to Carbon-nomex-carbon composites on the x33 space plane. And every material in between.
DOD specifies in a way that only the most expensive materials will do. Even commercial aircraft single blades on jet engines cost $15K EACH.
https://www.mdpi.com/2504-4494/4/4/101
BTW that artillery gun barrel has a steel liner. (titanium is too soft and lacks fracture toughness) so there is a very expensive bonding process that has to be done