To manage your expectations, your question should really be around what F&B the lounges serve at individual specific hotels in specific territories because this is highly variable. You cannot even determine the lounge service standards by brand within Marriott.

As you're new to this, you can be forgiven for not knowing that RCs do not provide lounge access. This, I believe, is because their lounges are a significant cut above regular hotel lounges and provide effectively full board at high quality. I've never stayed at one so I don't know.

Elsewhere, apart from the Ren St. Pancras, you'll get access at the brands according to the T&Cs as you've identified. It's not a matter of discussion. Your experience is highly variable depending on the country you are in rather than the brand with SE Asian capitals the best at providing a great experience. As you're heading to Japan, I'd suggest a side trip to Bangkok to experience proper lounges with proper food and booze in the evening.