You're correct, however China is rapidly closing this gap. They've recently been actively training for beach landings and deployment using roll-on/roll-off (RO-RO) ships. To your point, 100 miles is a lot and those waters will be contested. But China knows that, and they're dealing with that too. Specifically they've massively expanded their land based offensive ballistic and cruise missile capabilities for both anti-ship and land attack. From the link:
Now you might say our anti-satellite, EW, jamming, and cyber capabilities make that issue moot and break the kill chain. You willing to bet 10,000+ sailors' lives on that? I don't think Biden or the Navy will be, and for that reason the SCS and Taiwan straight will be relegated to subs only and our carrier strike groups will be held at standoff range beyond the first island chain. We'll need 3-4 of them minimum and all the associated logistics that go along with that.
At the same time, Guam and Okinawa will also be saturated by those missiles. We don't have enough anti-cruise and anti-ballistic missile defense to make up for the sheer numbers that China can throw out today, let alone tomorrow. If China gets serious, Guam and our other major Pacific bases will get cratered. This is why our recent news with the Philippines to open new and reopen old bases there is critically important to spread our assets. We can't keep all our planes hot seated, fueled and ready to take off on a moment's notice 24/7, so the AF is going to lose a shit ton on the ground. A recent wargame found that ~90% of the AF's ~300 planes lost were destroyed on the ground. We also tended to lose around 2 aircraft carriers and about a dozen ships in total. That sounds unfathomable, unthinkable. Our USAF and USN are too good right? I'm sure the French had similar thoughts about the Maginot line.
OTOH, China has issues too. First they lack experience in amphibious landings, and that's really hard. We paid for our learnings up to Normandy in blood. The PLAN, PLAF, PLARF, and PLA haven't demonstrated combined warfare (yet). Their top-down culture is risk averse.
Pros for China:
Homecourt advantage
Nationalistic fervor
Easier supply chains
Asymmetric advantages in missiles, potentially cyber
Quiet diesel subs good for cross-straight and near costal fights
AA/AD in SCS
Enough nukes to hold us to MAD
Cons for China:
Technology disadvantage vs. US/allies
Economic considerations of fighting one of their top 2 trading partners (this goes both ways)
Lack of experience in amphibious landings
Taiwan's geography works against them once they land (few viable beaches/ports to land at, lots of mountains and choke points make it defensible inland)
Time - the longer it takes the worse for China once things go hot
Pros for US:
Overall much stronger military, better training and more professional
Technology advantage in stealth, standoff weapons, anti-missile defense (although #'s limited), anti-sub warfare, space, and others
Blue water Navy
Cons for US:
Military is currently spread around the world
US population isn't bought into the need to defend Taiwan or spend our lives on another war in Asia
Could go nuclear
Long supply chains make sustainment really hard
Relatively low supplies of anti-ship standoff range missiles like LRASM, which forces the USN to either put subs or carrier groups at risk
Unlike Ukraine, Taiwan cannot realistically be resupplied once the conflict starts because we cannot guarantee air superiority due to mainland China's missile reach and proximity
Limited basing options in AsiaPac make juicy targets for Chinese missiles + our antimissile defense is nowhere near enough to deal with their #'s
If you really want to geek on this stuff, read the output of the Center for Strategic and International Studies (CSIS) unclassified wargame "The First Battle of the Next War - Wargaming a Chinese Invasion of Taiwan" released in January 2023. It's a sobering look at what we face. The bottom line: in most scenarios Taiwan is able to sustain as an independent democracy. The bad news: we lose a lot of lives and materials and our military is severely degraded for years to come (as is China's).