Crafting feats do wonders, my present build has most of them (have the one for leathers, fabrics, ballistic panel, and guns). The fabric one is good if you use tabi boot variations or normal, light leather boots. Sloping does nothing for vests afaik. The 20% quality boosts is mostly felt with late-game things and the already high-quality things get that extra. Got up to 40% / 12 mechanical armor stats going on while maintaining 100+ evasion/dodge and 0 encumberance thanks to self-crafted, quality materials.
By lowlife I think he means low constitution builds? Mine is 5 constitution btw, and other than some instances where I have to watch for annoying entangling+critically shot with a bow bullshit, don't usually have to worry about hp.
So far, I find kevlar/blast cloth to never be worth adding as the bonuses from them seem atrocious for the increased weight penalties, so cannot say how those might be effected by Tailor. Thinking on it too, really, the tailor feat might be a waste for non-entire crafter, because feels like fabrics are woefully underused so the feat slot might not be worth it to you.