So, two problems. First, this would be heavily rewarding to tanks that can use both stats, which would put them in a position above tanks that can't. It would also help bruisers a lot more than it would help tanks. Neither of these are particularly desirable.
Second, the entire problem with Atma's was the old passive. Giving people a damage reward for building as tanky as possible is not good design, unless it is built into a kit. Back when Atma's was strong, it was a major problem because a bruiser could pick up the item and build as tanky as he wanted while also having enough damage to be a threat. The old meta golem and fratmog's builds were extremely annoying to play against because someone could get ahead, be unkillable because they had nothing but tank, and still rip a hole through your team.
If you build tanky, you should be getting tankiness. If you want damage and tankiness, you either get a damage item or you get an item like sunfire which isn't as efficient for defense as other options. There has to be a trade-off. If I'm getting everything I need from one source and eliminating all my weaknesses, that's bad design.
Atma's old passive should not be on any items. There are better ways to reward champions for building tanky.