No, you are not listening, China diversifies channels of oil import by choice, not a must, China can stop importing oil from any country and increase the amount form other countries even now today, what they sell to China is far from their capacity, it's the oil suppliers courting China and want China to increase their share, not China courts them. If push comes to shove, China can import more from neighoring country and turn to tap her own oil resources.but again, US blocks the strait is very unlikely today, and will be more unlikely in the future cause it may lose the ability to do so.
Bangladesh doesn't have to worry about China, If US really wants to block the strait, it can do so with or without Bangladesh, so you are not really that make or break important.
OK, let me explain another way.
Say USN blockades China today.
That means only 2-2.5 million barrels of oil can reach China from Russia and Kazakhstan. China now needs to make up 6.5-7 million barrels of lost imports.
It has the following options:
1. Use it's stored strategic reserves but if it uses this it may not have enough left after only a few months for it's military to fight the US if it comes to war.
2. Tap it's own reserves to increase production but that would take maybe at least a year to pump even 1 million extra barrels of oil
3.Ask Russia and Kazakhstan to pump more oil if possible through pre-existing pipelines. They may be able to pump 0.5-1 million barrels extra but any more would take time and substantial investment.
USN will not blockade you alone as JN and IN are likely to join in.
USN base in BD will mean that Bay of Bengal will come under US control and so Myanmar becomes useless to bypass Malacca Straights.