Honestly, the benchmarks by Peter Cotton are more or less garbage. Prophet performs well with specific types of time series, like the one I mentioned earlier, which aren't included in Peter Cotton's benchmarks. If you have a time series without a clear trend or clear multiple seasonalities, and you can forecast it in an autoregressive way, it's obvious that Prophet won't work well for it, making such benchmarking entirely pointless. If you have mastered forecasting algorithms and understand when to use them based on their peculiarities, having a library like Prophet in your toolbox is still useful.
P.S.
I haven't used Prophet in a while, but according to the Git history, it seems that the latest versions have been significantly sped up. Additionally, Prophet can be easily parallelized using Spark or other distributed computing platforms.