I don't buy this argument.
There's a difference between convergence of UX/UI patterns (which is generally a good thing) and visual design - layout, typography ect. which seems to be what the original tweet was aiming at.
I think the convergence of visual design is more a symptom of agile/rapid development practice and the popularity of CSS frameworks.
Instead I believe we should see sticking to conventions as the sensible option. We should see it as the thing good designers do. That we should have a good reason for breaking with these conventions. A reason better than us tiring of designing within the same old constraints.
Hits the nail on the head.