This type of user is one of the reasons the mempool limit is still useful, Memo 😙
Especially when these wasteful actions are being performed with faucet funds
Any 'Faucet' funding facility is best implemented with layered limitations. Indeed - the mempool limit does help. A faucet 'queue' may also help. 1 or few posts per block?
One other idea occurs: An "unfunded posting page" where new accounts could test-submit what they propose to post "We" could sponsor such posts that have merit, paying the tx fee.
It would require a new page or sub-section under 'feed'? where unfunded posts could be triggered by sufficient tips - which then pays the tx fee. make sure OP gets subsequent tips.
In this ephemeral fashion objectionable material may fail "the sponsor test". After some timespan (24hr?) unsponsored material would simply vanish. (This is only for the unfunded).
This - I meant to squeeze in that very important aspect: Limits set by the mechanism sourcing funds. (as opposed to "baked into the protocol" which would be disastrous)