There's nothing stopping a campaign from running the whole war. The devs just didn't fill that part out. Players have the Mission Editor and can expand the campaign if they want.
So saying that SH5 sucks because it doesn't have the whole war is really just being short sighted. When people talk about the end war in SH3, they sure aren't talking about the stock campaign. They are talking about a reworked modded campaign. The exact same thing you'll see with SH5.
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