The bomber belong in what, ~1940ish while the mech inf is at least 20-30 years later if not more. The game fails to reflect this.
And even with the upgraded yields, it's still going to take a really long time to build things. Your city here has about 30 hammers, and that's with every single citizen devoted only to food or hammers, nothing else. It's a fairly large, pure production city, and it'll still take 10 turns to build an infantry or anti-tank gun.
It's a fairly large, pure production city, and it'll still take 10 turns to build an infantry or anti-tank gun.