Lighter is always better, for experienced no doubt, but also for beginners.
So if a foil is nervous (jittery) it is not because of lightweight, it is the design that is like that.
Nervous can be the same as "lively and good" for the experienced though, and bad for the beginner, so not that simple.
The deduction one could think beginner foils that are heavy and stable, thus heavy equals stable, is tempting, but IMO plain wrong.
Beginner foils are heavy because they are cheap, and they have to take a lot of abuse so also stronger in terms of "bashing".
And as beginner foils are designed, hmmm - for beginners?, they are more stable, meaning bigger stabilizers and in general.
A lightweight foil is much easier to carry, and also a lot easier to waterstart (especially for these few who want to learn strapless) so much better for a beginner.
But, as you dont turn or anything, when learning, the heavy foil when up riding does not have any drawbacks, agree.
When experienced, for turning and jumping (and pumping), heavy foils suck bigtime - but we all know that.
Light is expensive yes, and if one has never used a lighter foil (same stability design that is) - dont try one, as you will want one
Heavy foils works great, when learning, and also later if you have never tried a light one, as simple as that
PF