Oh I agree. What's convincing to me is the momentum. The DataFrames.jl team only started focusing on performance three months ago after hitting v1.0[1] and were able to rapidly become competitive with groupbys; the performance of join is next[2]. Compare the live view with the state when grandparent's blog post was written/updated (March of this year).
I expect it to continue to improve; note that it's starting to be the fastest implementation on some of the groupby benchmarks.