Yes though I think taking all this stuff into account: freedom of effects vs. limits the current system is quite good at preserving the sound of and focus on the synthesizer itself.
Then again...
https://soundcloud.com/xhip/farrest
Here I've used only a single master limiter which is active about 1/1000th of the time to limit a few small peaks allowing +3 dB gain, otherwise the whole mix would be -3 dB and there would be a few small instances of clipping adding high frequency content.
So limiting effects doesn't always make a lot of difference where synthesizers are designed with built-in effects. Unless the rule goes so far as to disallow use of any effects; even a built in chorus?
If anything perhaps "no presets" might be a good rule. Although this would make the focus more about the synthesizer itself rather than the preset banks available it would potentially also be a little unfair to those with less skill in this area. So it's all another trade-off that I think is handled well with the current "anything goes!" rule. Although authors should feel best creating totally unique presets this could eat up all your time with a synthesizer and you'd never get any melody composed.
