With the usual caveat that I don't actually care if the writers are good economists so long as I get my neon awesome...
It doesn't work the same in other countries, but those countries don't actually generate the revenue streams or the supply chains the the CP megacorporations take for granted as to why they're so big and powerful in the weak-central government world.
I think in general people really lose their conception of scale for money and supply chains once you move up to the sizes we're talking about.
Since you mentioned US firms doing the war business thing, the last 20 years have cost a little over $3T in either Overseas Contingency Operations or OCO-specific Defense spending. At peak, LOGCAP (essentially, for forum purposes, how you pay Keller-Brown-Root, Haliburton, Dynacorp, etc) contracts were $15B a year, and today's continuations are at $8.2B a year. Thats total cost amongst a minimum of four "prime vendors" given the year. As much fun as it is to declare crony capitalism, war profiteering, etc. (and there is some truth to that) the reality is that the guys hiring third-country nationals at low wages, storing them in tents at near sardine conditions, and using them to do their dirty, dull, menial work for a client who is essentially showering them with money - and by the way, in cyberpunk doesn't exist to do that because its a weak government - these guys are making chump change. Maybe $3.75B of revenue if you're really lucky. Lets imagine a ludicrous margin where half of that is profit. $1.88B.
Berkshire Hathway holds, in apple stock alone, $117B.
At $570B Amazon is valued at more than the sum total of payments to American companies involved in the war zones proper for the last 20 years.
Saudi Aramco, essentially Saudi Arabia's national oil company with the rights to all Saudi oil, was at it's highest valued at $2T (that's $2,000B). A lot of that is a global plurality of the oil supply. It has since been surpassed by Apple. The guys who sell you your Iphone are worth, give or take, 1,000 years of LOGCAP profit for a company.
It would take that evil war zone (ok, mostly they provide laundry and cooks) company 2,547 years to fund the USG FY 2020 budget. If Amazon sold every last share and asset, they could afford 1/8 of it. Selling off all of Aramco or Apple won't get you to half.
And once we get up towards the people who even have a vague chance of wielding megacorp like power, you become entirely dependent on functioning global supply chains and markets, dominated by more or less global security covering the commons, and strong rule of law combined with disposable income for billions of consumers. (There is a great paper from the 1950's called "I, pencil" that shows just how much of the world is involved in turning your pencil into the practically disposable schoolboy item.)