I agree with what you’ve posted and believe it’s good advice, my point re. calcium is that they won’t over consume it given the choice and there is no harm offering it separately so it’s there for if or when it’s needed.
I think there’s a bit of confusion over what is offered separately and what is effectively force fed/mixed in with the only available food.
As you’ve suggested a balanced blend if added to by more than 10% will no longer be balanced, in order to increase the protein levels in chicken starter to the necessary levels required for a quail you would need to add more than 10% insects which would reduce the overall available calcium below the desired percentage as oob child’s chicks have demonstrated by picking at it in small amounts.
If mealworms are used solely to adjust the protein levels this would also negatively impact fat levels so crickets would be a good addition to offer along side but protein levels are lower in crickets than mealworms so an even greater percentage would be needed to achieve the desired level of protein, further reducing the level of available calcium.
I’m happy the op is getting the appropriate food and this seems the best option unless a wide enough variety was being offered for them to balance their own requirement.