You already have the stainless steel so you might not like this idea but restaurant quality stainless shelves come in a lot of different sizes and have the rounded edges/drip edges already built in and no need to worry about bonded material etc. We bought three sets and they are extremely strong and look good. Probably not “several people sitting on them strong” but actually with the right number of L brackets they probably would. They aren’t really going to work with your inside corner with rounded edges so it’s likely a non starter though but there are flat edge ones that might.
This is where we got ours.
Max 16” deep with up to 96” length. Omega Stainless Steel Wall Shelves 18 gauge - Various Sizes
This is where we got ours.
Max 16” deep with up to 96” length. Omega Stainless Steel Wall Shelves 18 gauge - Various Sizes