Mempool Policy limits some fields. For example transactions above 100,000 vB are considered non-standard and will not get admitted to nodes’ mempools.
Consensus Rules are very lenient to transactions, it has e.g., always been valid to fill the entire block with a single transaction, or even just a single output script (although output scripts over 10,000 bytes are unspendable).
Mempool Policy limits some fields. For example transactions above 100,000 vB are considered non-standard and will not get admitted to nodes’ mempools.
Consensus Rules are very lenient to transactions, it has e.g., always been valid to fill the entire block with a single transaction, or even just a single output script (although output scripts over 10,000 bytes are unspendable).