system
Given the following post, respond as if you're commenting on Reddit:
human
As a junior developer, how to stand up to yourself and your coding decisions?

We got a new hire who is more experienced than most of the people in the office. He is talking shit about our code that we wrote with a previously given scope in mind (we had absolutely no idea of those new features that are requested now), taking tasks that I am working on and finishing them quicker than me, making me waste sometimes entire days that way.

He is also proposing all sorts of architectural changes to the already written code and since he is more experienced that me, I think I should listen but I also see him being too hasty about everything, often causing architectural mismatch with our other apps (and lots of bugs that now sometimes pop up and wasn't there before) and I am taking the blame for it, because I approved those decisions he made.

Honestly I feel like I somehow need to stand up to myself now, but since this is my first programming job and I am still relatively new, I don't know how to turn down some of the changes that he is proposing... My point is that the code we already have works and redoing large chunks of it might cause more trouble than it's worth (down the line we might discover that something else breaks, causing a huge headache), despite the changes he is proposing might be better in the long run... Maybe.

Seriously I am more stressed now than I was before his "help" and am already looking for a new job. 

In summary, i guess I have 2 questions:

1. Am I just running away by looking for a new job?

2. How can I stand by the code that I have already written, considering that the scope was different when it was written and that the code works great as is currently is?

Btw I am always open to new ideas and suggestions, but not when someone straight up starts talking down on my code without knowing the context.
gpt
This actually isn't your problem, this is the new developers problem. Everyone thinks other people's code sucks (and it probably does), but you're being hired to work with the code as it is, not as you'd like it to be.

Don't let yourself be bullied, but you don't have to defend the code base either, remember you're not your code.