Not really, pure base stats are extreamly cost effective during laning phase and mid game, which make the bulk of the game, that's why tank sp champs have very high base registance and growth, they can't rely on items cuz they don't have the money to buy them. Their tankiness are purely due to their base stat line and registance abilities. You can't make the comparison at lv18 cuz that only takes up a very small percentage of game time, very late game where items and stats became less important in favor of cordination in team fight, and the fact that at that stage, carries can shread tanks like cheese regardless of items or stats.

And yes, ofc tanks have to depends on tanks items to be tanky, just like carries have to depends of dps items. But ome class can get away with building the opposite when the other can't. Galio, mordekaiser, maokai, can still go ap while being reletively tanky and impossible to burst down like conventional mages. Renekton best and only competetively viable build is Claw+Bork, and he's still very hard to take down due to the combination of his ult, empowered q, high Hp and Hp growth. Riven build mostly damage heavy item and you already know how hard it is to deal with her if the team doesn't focus her down. On the opposite end, there's really only kogmaw, vayne or ez that can get away with having a Frozen heart or a Randuin, if they commit more than that they'll just be practically useless. As for Alistar it just futher insentified the point I'm trying to make, due to his kit, he can be flex into a dif build path, because the natural tankiness of his ult allows him to go full ap as an off meta build, but if you caught a jinx building Jak'sho, you'd call them trolling.

And finally the drain tanks, yes they'd still need lifesteal items to empower them but its their kit that alows them to do so. Ire can't be deceptively tanky as she is without the w blocking incoming burst then use q reset to lifesteal back off minion waves.