Linguistics is mostly descriptive, mind you; it doesn’t “make” things correct, it explains what happens.
That said, “are belong” wouldn’t work. “Belong” indicates possession, not a change of state, so even under older grammatical rules you’d still need to use “have” with it. And you’d need to use it in the past participle (belonged), not the base form (belong). Note that Oppenheimer’s quote doesn’t have this problem because the past participle of “become” is still “become”.
And the present perfect wouldn’t even make sense here. CATS is not saying “those bases used to belong to us, and they still do”; it’s more like “those bases used to be yours, but now they’re ours”. You’d need to use the simple present here, “belong” - “now all your bases belong to us”, without an auxiliary, with the “now” highlighting that this wasn’t true in the past but it is in the current time.