Really depends on what you mean by ‘hard’. There will be use cases where that justification comes easily.
This is another way of saying: “There are no solutions. Only tradeoffs.”
This is a way of saying: Blockchains solve nothing in particular. But they do offer some novel tradeoffs.
This is a way of saying: To get the greatest benefit from all the tradeoffs available… think of the unit of development as the relay chain.
Did anyone actually propose this?
If they did it’s not that we should poke our tongues at them.
Rather, they likely have a set of tradeoffs in mind whereby they can imagine living with on-chain remarks. Some obvious tradeoffs are no vs some storage nodes, don’t tie your staking yield to the chain RoR, etc.
They also possibly haven’t embraced the idea that the relay chain is the unit of development. In which case they are in good company.
Of course, there is another set of tradeoffs involved in deciding whether the benefit to them of on-chain remarks is worth the tradeoffs of a permissioned chain, or a permissionless chain.