While I'll say price is a very important sticking point (look at the results) I'll put things in this particular order:
#1 Diodes brand & model
#2 Diode Quantity
#3 PPFD (why you say #3? Because PPFD is huge, but it needs some middle ground, high PPFD output isn't everything, the spread/angles/shading are far more important that sheer numbers). Ideal PPFD ratio allows dialing it down on the plant, increasing overall efficiency. Spread out = better, period.
#4 Price
#5 Bar Quality.
I have a problem with #4 and #5 because both are important. I love the bar quality of the SF upon unboxing, because it's way, way more durable (although somewhat more heavy) I think you went the correct route on this front... Bottom line, it's durable, and the interlocked square config, (adds strength) plug design are smart build quality.... I think for price sake, (and overall durability) you need to stick with the steel construction. Some people take shit down and put it up again, constantly on the move (a new grow room) it needs to withstand handling.... You've accomplished that part very well. Perhaps overall weight can be reduced in design upgrade down the line somehow. Can't imagine what all aluminum frame would cost, but it's certainly prohibitive.
I would suggest looking into composite materials, possibly, if they are within reach, price wise, if strength can still be assured.
Great Job BTW, I'm unboxing right now. Both lights are fantastic builds and I've seen a ton of LED builds over the years.
PS: I really like the clamshell design on the ends, and the added length between the driver and the diodes, very smart... Highlights your attention to the fine details.