Ultra long haul flights in 787 being weight restricted is a common thing. I pax to HKG often and it's happens a lot that 50 seats are open but you can't get on because its weight restricted. Sometimes they can wiggle you on in the end sometimes not, but it's common to have to sweat it.

787 was never designed to carry heavy loads of cargo AND heavy loads of pax and go ultra long haul. Never designed to replace the 777, so it unsurprisingly can't.

777 was never designed to replace the 747 and it unsurprisingly couldn't. 777-300 has 50 seats less space than 747-400 and 100 seats less than 747-8i. An effective capacity reduction.

Fuel capacity has a lot to do with being weight restricted. 787 wings are maxed out. No space left to expand it's fuel capacity. Thats why 787-10 range is a joke compared to the A350-1000.

A350 is one notch more capable of an airplane than 787 with a lot more fuel capacity and heavier weights... longer range. 777-X variety is one notch more capable than the A350.

Its a mistake to have the 787 as the exclusive ultra long haul airplane for a serious international airline with nothing more capable in the fleet. It automatically cuts us out of certain markets and limits our capacity to lift payload when we do fly into certain markets which others will no doubt happily lift instead.