It doesn’t, endurance only affects damage to health.
I think that would probably be fair for builds that use both health & ward (ie, not low life).
Low life builds aren’t the issue. Specific skills that can generate massive amounts of ward on demand are the issue. A “proper” low life build with, say 4k hp, both body & boots to generate 35% would have a stable ward of ~10-11k & a max generation of ~700/sec.
You can’t. Exsanguinous converts 20%, Last Steps of the Living converts 15% & the experimental gloves affix can convert anywhere up to 12% at t5 or 20% at t7 (good luck finding one of those on a decent base with other decent affixes), this would be a total of 55%. At most that would give you ~5.6k stable ward with 2k hp (& 200 ward retention). Low life ward conversion needs much more hp to scale into ward than you think it does.