Other than hot faces, the way to make SL sets a bit better is to do a better job with the COG of each club. The 6 iron should not be the same as the GW. Longer irons should be more offset, lower profile, lower more rearward COG. Wedge should be less offset, higher COG. Intermediate clubs would be in between, of course. I've done my DIY SL set like that to the best of my ability, and it's an improvement.
And I agree that they should be heat treated for greater bendability.