i 100% agree with you on those flatline rubber tabs absolute garbage
you can get the flat rubber by the pound here in 3 different colors https://fishingskirts.com/product-category/old-school-square-rubber/ i use living rubber on all of my hand tied jigs switching over to this flat rubber if i can find other colors like blue, red, and purple.... i am 95% sure this is the rubber you started the thread about hope it helps