if they continue to follow the rules and be reliable, more of the world will be willing to expand relations with China, protecting them from the US or anybody else acting unfairly

I feel that this is true to an extent. If you are a government in Africa or a company in Singapore, will you prefer to do business with the guys who have a track record of keeping their word, or the guy who changes his mind every second day?

Besides, if China openly flouts the blockade, how sure are you that Trump won't start WW3? Better to just deny any new weapons and wait for the old ones to rust.