I think the likelihood of a kinetic attack on Ramstein would be much lower than a kinetic attack on a joint Australian/US base. The reason being that a kinetic attack on Ramstein would trigger NATOs article 5. Cyber attacks below article 5 threshold would be likely though.
I don't think article 5 deters China at all. China doesn't want to invade NATO, it wants NATO to bend its knee to it. Ultimately, it probably expects NATO to place its security arrangements with China, and kick the US out of NATO.
China isn't going to launch a tank charge through the Fulda gap. They are quite able to make devastating strikes from China without ground forces. China throwing its soft and grey power around is a real thing, and something that would on its own, likely crush some NATO states.
Its clear any action China takes on Taiwan would bring the US in immediately, and likely US allies, which include the UK and Canada and US and Canada are way down on the threat list to China behind things like South Korea and Japan.
Take the US, Canada and the UK out of NATO, and what extra expeditionary capabilities does NATO field that would be able to rock into China's doorstep in a meaningful way. Would they even be able to make it there if China encouraged some other actors to annoy NATO forces outside of NATO territory.
And how happy would NATO nations do that if the the US is loosing 50 fighters a day and 5 destroyers a week, Guam being laid waste and bare taking heavy losses, while Korea, Japan are taking loses in the thousands per day.
This is assuming Russia is just sitting there, doing nothing in Eurasia while the rest of the world breaks out in chaos. NATO may find it strategically more comfortable to only put Russia on its war list.
Yes, E-3 is out of date. But it's a hell of a lot better than nothing & not counting the USAF there are 20 of them operating in Europe, & it isn't the only AEW aircraft operating in NATO or soon-to-be-NATO Europe: there are 4 Turkish E-7, 2 Italian G550 CAEW, & 2 Swedish & 4 Greek Erieye, plus 3 French navy E-2C.
A replacement for E-3 should have been ordered years ago, for the reasons you give, but at least something's being done. Italy's getting more G550 AEW, Sweden's going to replace its current SAAB 340 Erieye with Globaleye, & perhaps increase numbers, & the UK's buying E-7 (converted from secondhand airframes to speed up delivery, in addition to plans to replace E-3 - eventually.
But there is a giant big capability hole.
Currently look like being filled by a non-NATO country located very far away. One that the EU sees as a trade threat greater than Iran or China or Russia.
And yet we are being told to all sign up to NATO. The thing we outside NATO, are propping up.
But I am not sure article 5 mean much to a power that intends to wipe the US out of the pacific, wiping the US off US territories like Guam, and is located in Asia.
Both the US and UK panic buys aren't exactly filling people with confidence. Sweden is literally just joining NATO now, Turkey is half out of NATO, and at high level tension with Greece. Turkey and Greece invested in these capabilities because they knew NATO doesn't prioritise their security needs. Two Italian CAEW which were bought partly for work offset reasons (Aermacchi M-346 sale) its hardly mind blowing AEW capability.
Getting back to Germany, Germany should be looking at making itself a bit more of a complete spectrum force. Those forces/capabilities can sit under NATO command, but be maintained by Germany, and ensured they can be tasked for needs by Germany if required.
NATO AEW capability is a perfect microcosm of issues within NATO.
