Double dipping or more into defenses is part of why we have damage creep right now

currently (and in the past):

• tanks/fighters get to enjoy high HP as well as high resists
• Shields and % damage reduction feed into their already impressive effect health pools, multiplying their defenses (sustain too, to a lesser degree)
• Some tanks/fighters get to directly turn their durability into damage
• Fighters have had a particularly bad habit of being better with tank items than tanks
• Things like HP regen that work better over a longer period of time shifted aside in favor of more immediate, 'noticeable' effects - allowing tanks to deny aggression at a moment's notice with decent reaction if they have on-demand shielding or % DR, making more 'noticeable' moments of power that effectively void aggressive play altogether

Since very old ages we've had several "band aid" responses that let everyone 'counter' this stuff instead of Riot just directly addressing the issue. Things like;

• Percent damage, which despite being a very powerful mechanic is laughably commonplace now, even on tanks
• Armor reduction everywhere (M. Pen is ridiculous, too but it never got MORE common as a response to high durability)
• Out-right ignoring otherwise absurdly high defenses through means like true damage (IE, Conqueror as recent examples of the offense)

Any way that could actually fix the issue of the eternal arms race is far beyond a scope that any of us or anyone at Riot would like to accept. I'd just like to remind you that we've had many instances of the other end of the spectrum and that there's a reason Riot isn't keen to letting it return; we were equally dissatisfied with tanks being untouchable while steamrolling squishies as we are with new-age fighters being pseudo-assassins.

That said, I'd still like to suggest that perhaps the easiest way to fix things is actually less and not more. Simplifying tank stats and reducing the amount of amplified defense that comes from kits and items (alongside reducing the above bandaids if not removing outright) could potentially be a big step in fixing the issue.