I don’t know if it’s standard or not to get priority luggage as a silver member, which I am, but I have always had a priority tag if I check in using the business class checkin (which you can do).
Also randomly at times my luggage is tagged priorty when I go through standard checkin.
The trouble is that BA is very popular still, and I see a lot of silver members. It wouldn’t be much priority on some flights – I’d imagine London to Singapore is heavily business related, so in essence everyone becomes priority.
I flew Singapore Airlines from Jakarta to Singapore last week on their A350. A short flight and they were very good, but I didn’t notice a huge difference with BA on that one.