The 100k vbytes refers to the total size of the transaction including witness data, headers, the inputs and outputs, etc. For inscriptions spammers use the witness data aspect of the transaction. From my understanding, each input has its own witness field, which can carry only a limited amount of data. To include larger files, the data must be split across multiple inputs and/or multiple transactions. The total transaction size cannot exceed100k vbytes.

How much bigger percent wise can one input in the mempool be after this? Is this a concern?

0% max block size is 4mb since 2017.