I personally think tethered caps are fine, pretty sure they objectively reduce wild trash/lead to less cleanup requirements behind tourists and the like.

Do you think that the cost/benefit tradeoff in untariffed Chinese cars would be significantly better than tethered caps or deposits on bottles, or banning throwaway plastic straws?

Because this is far from clear to me; sure, introducing more, cheaper electric cars would help much more than reducing plastic waste, but the cost/risk to local industry is also MUCH higher, and a situation like the one with agriculture (a whole industry sector running basically on subsidies, in every industrialized country) is worth trying to avoid, too.