Solutions
The general ledger should be boring.
On both of our paths, the general ledger is Microsoft Dynamics 365, localized for each country. The principle holds either way: the general ledger should be boring. Agency complexity belongs in software built for it, never configured into the ledger by hand.
An office in Paris keeps books that satisfy French requirements, not an approximation of them. The same holds in each country where an agency works.
Business Central is where most agencies belong. Finance & Operations is for the largest, when enterprise requirements demand it: high volume, several entities, complex commissions and royalties.