I wonder where you got the 354 MB from. That's wrong.
Currently, there are around 150 MB of transactions waiting for confirmation in the mempool and even a transaction paying only 1 sat/vbyte should be able to enter the mempool of any node.
You are mixing up your numbers here.
The 300MB limit is the RAM usage of the deserialized data for all the transactions in the mempool. This is not the same as the space that these transaction will take up in a block (either in terms of virtual bytes or raw bytes). Of course every node has its own mempool, but even identical mempools would result in different RAM usage between nodes due to different hardware, node software, OS, and so on.
Although we currently have around 127 vMB of unconfirmed transactions in the mempool, when deserialized these transactions are using around 300 MB of memory.
Here is a good site to visualize this:
https://statoshi.info/d/000000020/memory-pool?orgId=1&from=now-2d&to=nowThe green line in the top graph shows the total transaction size, while the white line in the middle graph shows the memory usage of those transactions.