The mempool is not a global state. It runs in the RAM of your computer when you run a full node. Most people have theirs set to the default of 300MBs, but I have mine set to 2000MBs, but I'm also running full RBF on my node. So if you send a tx at a higher rate, it'll either get replaced on computers with full RBF, or replaced on computers which are dropping low fee txs due to their mempool size limits.