Do we really need to assume that economy can't cope without naval shipping for a turn or two?
It's not a question of 'can economy work for a turn or two'
The question you should be asking is. "What does a factory do when they don't get the critical computer chips they need for a month?" The answer being they have maybe a day or two, possibly up to a weeks worth stockpiled. Then for the rest of the month they have a bunch of mechs sitting around without any brains, targeting, locomotion driver or anything meaning all the fancy weapons on it has no trigger. Turning the entire thing into a multi million dollar paperweight.
GDI smart grenades without chips? Sure there's likely secondary methods of setting them off, or at worst they can go back a generation to 'regular' grenades that don't need electronic detonation. But say goodbye to the onboard computers that fly those grenades into the middle of a room of nod soldiers. Before you could just toss a grenade in the general direction of nod and have good odds of taking out an entire squad. Now that same throw lands the grenade on a patch of concrete metres from the target building and explodes harmlessly.
Repeat that for dozens, hundreds of factories. And it's not just chips. It's parts, chemicals, even people. Tiberium harvested in southern france has higher ratio's of potassium, leading to easier and cheaper refinement into a variety of chemicals which are then shipped to where they need to go, far cheaper and more efficiently than putting german tiberium through a longer, more complicated refinement process to make the same chemicals.
And it's not one month. It's 3 months or maybe 6. You're potentially talking thousands of factories worldwide suffering delays and shortages.
GDI is built on the back of globalized logistics. The world order that sees the remnants of dozens of european countries, african countries, north and south american cities and asian nations all pool resources and work together to produce goods at the lowest cost possible to build as much as possible. And you're talking about ripping out a lot or even most of that.
To give the faintest idea of what that's like. Britain IRL cut itself off from the EU economy, just the change in law leading to added checks. Just a minute or two per lorry. But with thousands of lorry's a day on the border that adds up to massive queues, delays, expenses, fruit and vegetables going off before reaching the intended destination. Knock on effects on the economy, and the losses of billions of dollars worth of trade and revenues. Businesses failed. People lost jobs. Containers piled up in some places unable to be moved. While in other places entire warehouses sat empty.
There's a reason the most successful nod warlords are targeting our shipping, railway junctions, docks and harbours. Attacking our logistics. It's the single best way they have to hurt us.
And, It's not just raw materials, parts, or finished goods. It's food too. People can't go
Months without food.
And to a degree... Sure sea travel can be replaced, by planes, trains and trucks. But you'd need hundreds of planes, perhaps thousands to make up the shortfall in what you've lost from cargo ships. Something like one cargo ship for a few days along the coast turns into weeks for thousands of trucks.
Logistics is absolutely critical. History has proven this time and time again for thousands of years. And it's not just a matter of building alternatives. It's about having those alternatives already in place, ready, and even then any changes can send the entire system into chaos.
