I use fully synthetic Castrol Edge Professional 5W 30 in my 2017 TD6...not because it's recommended by Land Rover but because it's a premium oil brand that I've used and trusted for many years. It also suits the 3.0L diesel engine, climate where I live, driving conditions, etc, etc.
All those brands you mentioned are very good branded oils. Out of the 3, I'd chose between Castrol or Motul like you. Manufacturer recommended oil brands are just that...a recommendation. It's partly dependent on who makes the engine and where it was made...it's not really any more complicated than that.
Land Rover are a British company and the engines are Ford based, so a recommendation for a highly trusted British oil brand that figures big in the American automotive industry isn't too surprising.
Always use a quality branded oil and stick to it, that's a given. If Land Rover recommend Castrol Edge, then it's not a bad idea to keep using it. Along with regular oil and filter changes every 8,000-9,000 km or so, your engine as it gets older will thank you for it in the end
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