The intimidate nerfs "per se" didn't singlehandedly ruin intimidators. They are just one of the many things that have.I don't really go here but isn't this basically admitting that Landorus' waning in VGC had nothing to do with the intimidate nerfs?
What the intimidate indirect nerfs did was make a lot of Pokemon that were basically unusable cause of intimidate come back.
Most notably, the Urshifus would have struggled a lot more without their pseudo-immunity to intimidate, and pre-restricteds, Pokemon like Mamoswine, Entei, the various Defiants, were all but inviting Incineroar and Lando to come in and get nuked.
In fact, before restricteds, unsurprisingly Rapid Strike Urshifu had a lot of usage over its dark brother, as it could just ruin any Lando-T or Incineroar coming in and disregard the intimidate.
....the point I want to make is that they don't exactly have to nerf Lando, because the environment around it keeps getting harsher and harsher. Despite everything, power-creep exists for legendaries too, and Landorus is not a exception. Gen 8 has introduced a ton of outside-scenarios that make it worse and gen 9 looks to have introduced even more.