ideas for item changes

I have noticed that there are a lot of champions who do percentage of health damage with very few ways to counter it, building health helps a little bit but not too much and armor doesn't do anything if they are hitting through it and going straight to your health. Thornmail doesn't work anymore unless the adc, top and jungler don't have percentage of health damage but there are also a lot of champions that get on-hit magic damage items like the rageblade and thornmail is once again useless. I think thornmail should either be buffed in some small way or make a similar item for magic damage to counter things like devourer and rageblade, also randuin's omen stands out as a very useless item to me at the moment, it gives less than other tank items and the 10% crit damage reduction isn't much when the infinity edge gives 50% more crit damage on top of normal crit damage. Some small changes to a few items might make tanks tanky again rather than having them get gunned down by vayne, master yi or kog maw, i do understand the need to have percentage of health damage to counter tanks but i feel like adjusting some items would help make things feel better over all. Maybe make an item to reduce damage taken from true damage, an item specific for certain champs or comps that could give some form of build against champs that do a specific thing.

Throwing out random ideas for new items could create some useful items.