Continuation of the current policy is not a blunder. That is the most favourable scenario. Getting directly involved is an strategic blunder. Yes, it is unfortunate for the victims but it is not China duty to spend their blood and treasure to prop up a failing state instead of focusing on themselves. Besides, the only thing you will achieve in Myanmar is potentially weakening China which could be fatal
By this logic, China should also not develop say Xinjiang, Tibet or Guangxi because they're just historically poor and shitty so a lot of blood and tears effort was needed to bring them to developed nation status.
Myanmar is bigger than Ukraine or Afghanistan while being covered in huge forests. The Indians and Americans will not miss the strategic opportunity to turn Myanmar into China’s Afghanistan.
With transports from where? The most they can do is complain, especially after China already cut off India's side with the coup in Bangladesh. They complained already many times without result. Whether China embraces expansion is or not, they will keep complaining without much result.
If you think not getting involved is a blunder. Wait until you get deadlocked in a multi year war where thousands of disgruntled crippled veterans return and an increasingly dissatisfied public opinion. Perfectly ripped for Western propaganda and coup operations.
I don't see how the few 1000 Myanmar ppl that are crazy enough to take up arms directly at PLA and end up crippled for it is going to affect China's core lands politics. Maybe they will create dissatisfaction within the authority responsible for occupying Myanmar. But on the other hand, there will also be growth and poverty relief that was never there under the stagnating junta.
Remember Myanmar is not even like Saddam's Iraq. It is much more like Syria. There is little unified national government and when China goes in, it's going to do so together with local collaborators already set up.
It is just a question of will and ambition. The current admin's strategists don't believe in using colonies to boost the country's wealth, this is more ideological than 100% factual and evidence based thinking. The second point is if China has the working room to take on another poor province. The answer is maybe not today, but defintely yes in a few years, since all of the poorer core Chinese provinces are reaching developed country standard around now. They need a few years to settle in, and then China could seriously have the capability to take on developing a new province.