Funny enough, the ideal fighter for the Taiwanese is a stealth Viggen.
@VTOLicious Yes, the FAR-21 is fairly reasonable for Taiwan's use case, assuming that it's got a decently short takeoff and landing. Only problem is what engine to power it with. F414 is likely to get blocked by the US. So, EJ2X0 or M88 (my preference between those two is EJ).
The limiting factor for a small 5thgen fighter/interceptor/air police is the weapons bay(s), not the internal avionics bulk. Even Sidewinders are 10ft long, AMRAAMs/Meteors are 12ft. Nobody is making "halfRAAMs" like the Cuda or whatever, ~6ft long missiles.
In the event of a shooting war between Taiwan and PRC, Taiwan is going to need aircraft designed around carrying AMRAAMs internally, because they'd be getting resupply from the US of whatever US missiles are in play.
In all seriousness, something the size of the F35 is the smallest "light fighter" most places are going to buy for a 5th gen aircraft.