Why would you want to craft all legendaries for a spec to begin with? Choose the one that fits your primary goal, craft it at max level. Then, by the time you have gear for your off-spec, you can craft an R4 for that too. Or just go with an R1 meanwhile, if the effect is that good.
The system does encourage having a primary spec, yes. But that’s it, a primary. You can still have other specs, and be competitive with them, it will just take a little more time to craft the legendaries for those. Probably less time than gearing said spec, so no real disadvantage.
The system is much more alt friendly than anything we had before, dating back to Vanilla.