I've been working on winning deity domination but I have no idea how to get any use out of any other units besides bombers, helicopters, and tanks once flight is achieved. I weaken the cities with bombers, then later jet bombers, then take the cities in one turn with tanks and helicopters. It appears to me that all other units move too slow to be of any use.

Is there any way to yse Rocket artillery, Mechanized Infantry, and Machine Guns in late game wars that justify their unit cost?

I typically kill off most of my musketmen and field cannons and all of my bombards once I can build aerodrome districts, and use the cost in savings to build knights and horsemen/calvalry that I can upgrade to tanks/modern Armour and helicopters all at once using the professional army policy card (50% discount on upgrades).

But I'd think there MUST be a way to use machine guns and rocket artillery and mechanized infantry in a productive manner in late wars. I imagine machine guns with the double attack promotion can be used to mow down enemy units if you provoke enemy civs into attacking you. But it just doesn't seem worth it.

Why prolong the war when I can just spam bombers, 10-15 and with aircraft carriers and enemy aerodromes, take 2 or 3 cities immediately after declaring war, ideally including their capitol, and taking them all on in the same turn with tanks and helicopters before the enemy civ even gets a turn to fight back?

Do you guys use the same strategy for late game donation victories at deity level? Killing off musketmen, bombards, and field cannons once you either get to flight or at least have 4-5 bombers, 5 tanks, and 5 helicopters?