1. I don't see why not. 2 F-22's vs 16-18 other fighters. The two F-22's have a collective total of 12 AIM-120's and 4 AIM-9's. 16 missiles right there. Add the 20mm cannon, you can probably wax 1 fighter with the 480 rounds in the gun. All of this plus the fact that you probably never saw the F-22 coming.
2. The only times the F-22 was 'shot down' in exercise was due to a mulligan; a enemy fighter just happened to re-spawn, and placed his gun sights on one. While that fighter respawned and nailed one F-22, his wingmen were all shot down multiple times.
3. The F-22 is also a surveillance platform; it has a excellent radar and datalink capability, and has acted as a sort of a mini-AWACS to other non-stealthy aircraft, helping guide other aircraft into better positions to gain an advantage.
4. The F-22 on radar is about the size of a small bird. Easily small enough to merge into random clutter. This aircraft is designed for initial penetration into heavily defended airspace and achieve air dominance. That's why it is called an air dominance fighter, not an air superiority fighter. Just one can ruin someone's day and put a real wrench into someone's plans.
5. Chinese SAM's cannot cover Taiwan effectively; it would be at the edge of the range of current SAM systems in use and in development, and would have a low hit probability, plus you have both friendly and enemy aircraft operating in a not very large airspace. The risks of a friendly fire incident is extremely high for SAM batteries in these circumstances.
Not to mention that known SAM sites would be selected as targets for initial strikes; US doctrine in the past couple of years has been to degrade enemy air defence and C&C systems first to throw the enemy into confusion and degrade their ability to respond effectively followed by strikes against logistics, followed by strikes against military units. Destroying or degrading one's ability to achieve situational awareness and be able to fight effectively is a skill the US has honed over the years.
