There are posts from the devs that explains everything. Apparently the 5.0 update was huge.
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plebbit-js 0.0.7 improved performance by a lot:
https://pleb.bz/p/blog.plebbit.eth/c/QmZoZToHuUSz3zPF9NyPRHTarrLk6TbYVy4mvSa8gwweKW
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