New fighters, I often notice, make more of the weight of their harness than they really should
I agree to a point.
I wholeheartedly agree that light harness weight isn't going to offset the effects of poor health. You should at least lift weights regularly and be able to run a mile.
The reason I say this is because if you're young and full of enthusiasm (but not necessarily energy) then you'll get out there and exert yourself like you don't usually, and being that tired makes you miss what's actually happening out there.
You'll get armor bites all over your body, then come off the field and probably start drinking right away, and any lessons you'd have learned are lost at that point. Then you'll think about it later, and remember how tired you were, and think "Hey, I need lighter armor" when the reality is your kit doesn't fit at all and you need to change a bunch of fastenings.
Flash forward five to ten years, and you're not fighting anymore because it just wasn't as fun as it looks, and you never seemed to get good at it, when all you probably needed to do was move that buckle so that it's on the side of your calf instead of the back...
HOWEVER, the weight issue is sometimes very relevant. Particularly if you're talking hand-me-down armor. I remember one set of legs that were floating around our household in the beginning - made of 14 oz leather with 12g galvanized splints and a 14g cop. I also remember my future brother-in-law being the biggest of us and therefore the only one who dared to wear them. They were simply ridiculous overkill.
Of course, when he got them on he declared them crap because - you guessed it - they didn't fit and bit him everywhere.
It's been my experience that, outside of the plastic world, overly heavy armor is often executed poorly. Plastic is different because it can be executed very poorly and still be lightweight.
I think any armorer who knows what he is doing is going to pay attention to the weight issue. That's why you find so many helms which are 12g top and 14g sides - someone sat down and thought "hey, fighters hardly ever get hit in the side of the head, so I'm going to tone that part down and SAVE WEIGHT".
As far as scale... a couple ideas.
I put it in the same camp as maille. IMO It has its uses as-is in the SCA. Those would be aventails, skirts, and places where the armor is probably going to be held away from the body part it's protecting.
If you're talking about doing full-body, I think the scale by itself - particularly the tiny RL stuff - is a bad idea for the places that are supposed to be rigid.
When people wear full-body maille on the field I've seen them go two routes - the more common "put something modern under it" route (I'm finding recently that ABS is really inexpensive and super easy to work with), or the less common "put something period under it" route.
If you sew two layers of canvas together in 1" channels, then pack those channels tight with dryer lint, then that by itself will give you rigid protection (no, really, it will). Depending on how skinny you are, you might get away with 3/4" channels if it has light scale over it.
If you're making scale, it might be possible to triple up the scales so that what looks like three is actually one plate with three dags coming off it. I've seen references to that being done with Roman squamata. If you blow that up to SCA proportions - say 2"x3" scales - that means that you're using effectively 6"x3" plates, meaning the protection would be a lot better.