Don't think it should feel like a casual workout though. You need to put in the effort. The point of staying around a 70-80% range is that you can do it more often, and if you want to progress, you will have to augment volume/weight.
Training to failure is more of an old school approach, but very much like lighter training, it needs to be designed properly. Think of the conjugate system who'll push max strength 2x/week but the other two days are light-dynamic work days.
What Firas is saying has been around for a while though, Pavel Tsatsouline has been saying it for over two decades, pretty sure Firas even refers to him during the full Rogan episode.
Yeah I guess casual is not the right word. For me a good amount of effort is the max amount that can I put into doing a 5x5 exercise while trying to keep my last rep as close to what the first one looked like in terms of speed or explosiveness.
Exercise til failure works as well, but it has its place. It's doable but requires an extreme amount of will power and discipline if done constantly, which is something most people don't have.