I dunno. I agree it should end early on the basis that I don't particuarly enjoy SL as a concept, but it's hardly an unsalvageable concept or expansion in general. It definitely suffers from an extra long initial launch as opposed to the swift X.1 patches we have gotten before, but the content we have does function like it should, and I sincerely doubt that most players have gotten close to the bottom of their chosen covenants reward system, let alone 4. And that is without significant RNG like with the islands of 8.0.
Genuinely, what does SL lack that a "proper" expansion would have had at this point that wouldnt be new patches? BfA had marginally more content if you counted the two level and endgame faction stories as completely separate, and Legion had less by far.
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And honestly, if the SL power scaling systems is reason to end the expansion early then BfA and Legion has it beat by far, what with their boring grinds and obtuse RNG based means of power upgrades.
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If your argument was that they should end it early to focus their entire team on 10.0 to really make it solid as a means of regaining their footing after a lack of knockout releases then sure, but don't pretend like it is because SL is just that bad.