My question is what sofsynths have you played with? I have about 20 staples and I have yet to encounter any of the problems you allege plague softsynths. Don't get me going about copy protection, but except for portability hassles (computer to computer), I have had no problem with any softsynth I have ever tried.
Hypersonic2 won't run at all in Sonar 5 as a VST - it crashes Sonar - and as a DXi it runs 'sticky', i.e. slow and sluggish as if it's struggling for memory (I have 2GB). Despite repeated calls and forum requests I've had no help from the UK distributor (Arbiter) or Steinberg who seem to be letting the product die, even though it was only recently launched. Disgraceful lack of customer service. Stark contract with the support provided by Roland. NI's Bandstand runs ok if it's loaded in stand-alone mode and connected to Sonar with a virtual cable, e.g. Midi Yoke. But again, as a plugin it's far from smooth.
I haven't had trouble with the lightweight soft synths with small sample libraries, but their sounds aren't at all convincing for that reason.