Nobody cares how the mempool works because it's not part of the blockchain consensus, it is not a global entity, and first seen timestamps have zero relevance. More over, they depend on the system clock, which may be off, on the network latency (a node may have been offline) and so on,

Not sure what the hell you're trying to say, honestly. I already explained why it is implausible to convince anyone that some TX was broadcasted before some other TX, because the fee-rate is not an indicator of chronology, but of mining priority.