Thornmail vs Randuins, design issue

OK ok, so heres my issue with the current tank lineup.

So first off, i like what was done with making thornmail cause grievous wounds, that was awesome and solved a lot of problems. I have some beef with the attack speed slow from a design perspective (for reasons i gave here ages ago https://boards.na.leagueoflegends.com/en/c/gameplay-balance/JG3e52T3-issues-with-tank-itemization-no-im-not-promoting-tank-meta) but my current main beef is that it often is difficult to decide whether or is a more fitting purchase when dealing with most champs, and sadly I find myself often building BOTH to deal with runaway carries, even though they have a passive that doesnt stack...

let me give an example

say you're fighting you have to deal with massive crits which will be mitigated by AND massive sustain which will be mitigated by , now you can build both (which i find myself doing more than id like) but that means you are effectively wasting gold on 2 attackspeed slows that dont stack... but frankly its what I need to stay alive... this happens alot more often than id like as most champs who build crit also build sustain and vice versa...

(after some additional thought) I think the fundamental issue here is similar to the old problem with banshees veil, the banshees veil passive was really more focused towards a carry whereas the stats were tank. maybe should be converted to an item for squishies trying to survive the first crit burst by hard ad? and a tank version that doesnt overlap so hard with introduced? I would be curious to see what you guys think