I can appreciate that they wouldn’t want us to pick every damage buff with no drawbacks. Given Sub’s history of crazy stacking modifiers, they probably want to avoid what happened in Legion beta with DfA hitting for like 8mega lol.
But, as Pxb said, it feels a bit off compared to Assassins who can choose Tempest or not. Both specs have to take the basic “fan” spell, but after that, Sub pretty much as to spend 10% of their points in stuff that may be at best useless, or actually counterproductive (like Replicated).
Or to compare Sub to their floofy cousins, Feral has 2 oddball AoEs in the middle of the tree. But one of them (Brutal Slash) is useful on single targets, and the overall tree is more flexible with a fork in the middle just after “20 required” that opens paths to all 3 spells at the bottom. Meanwhile, Sub’s path to the bottom starts on the first row.