England's Province Layout Should Be Reworked
It's obvious that province borders in EU5 are a gameplay abstraction rather than a historical one, so I'd much rather see them optimized for gameplay.
Right now England is the only major country with four provinces containing only two locations, which feels unnecessarily restrictive. Another issue is that many of England's key RGOs are grouped into the same provinces, while the most natural locations for urban development are just across the province border. Those cities can't benefit from the province's Production Efficiency bonuses simply because they're in a different province. A good example is the southern containing 2× Iron, Wood, and Stone. All four are valuable RGOs you don't want to urbanize any of them, meaning you have to give up important province Production Efficiency bonuses. Simply moving one Iron location into Kent would immediately create a much more natural industrial hub around London. The same issue exists on the Welsh border, where Iron and Wood are locked together in another small province.
London also deserves another look. Middlesex consists entirely Grain locations, which means the only industry that really benefits from the province's Production Efficiency bonus is brewing. That feels like a very odd design choice for London. The Thames also provides only the minimum river bonus, which seems surprisingly weak. Likewise, London's natural harbor value of 0.8 feels unnecessarily low. If the harbor value is intended to stay as it is, then at least increasing the Thames to the second-tier river bonus would make sense. I also think EU5 should avoid provinces with only two or three locations wherever possible. Province layout has a huge impact on urbanization and Production Efficiency bonuses, so players shouldn't be disadvantaged simply because of an arbitrary map split.