Yes. You are applying two distinct comma guidelines consistently:
The commas around a nonessential element. (Purdue OWL has some examples.)
Commas (including the serial comma) separating items in a list of three or more elements. (Number 5 in this list.)
There is no standard guideline for what to do if the application of multiple rules leads to a ...
When the sentences are short, commas are sometimes optional. In all your examples, the commas you’re referring to make no difference to the parsing of the sentences.
But sometimes commas help or hinder the expression of your intent. Consider, for example:
Now I understand why you did it.
Now, I understand why you did it.
The no-comma version says that you ...
Punctuation is a matter of personal preference in English, but the basic idea is it reflects the position and extent of pauses if the sentence were spoken. In the example you quote the comma (between “grade” and “to”) is at a position where no pause is ever made. That, and that alone, is why it is incorrect.
In short, I would either leave out the comma before but or, if that bothers you, simply use different punctuation—such as parentheses.
Let's start from the simpler sentence and then add the extra information:
I am a man, but I cannot endorse your claim.
So far, so good.
Now, we want to add a strong, burly man as parenthetical information:
I am a man,...
This isn't a situation that there are any prescribed rules for to my knowledge. You'll have to make a decision and apply it consistently. My opinion on the matter is that you should ignore the commas around non-essential phrases rule in this case. In my opinion
stifling curiosity, creativity, and ultimately, progress.
is superior to the two forms in your ...
You are correct. "...who put salary first" is a necessary part of the description of "those" and so must be written without commas. The first version is incorrect.
Both sentences contain additional errors. There must be a comparative word such as "more" if the word "than" is to be used - and "in first place" is the correct way to use that phrase.
The most literal translation of your example which has valid syntax and semantics and is reasonably idiomatic would be something like:
People who love their jobs can more easily excel in their fields of
work than those who put salary first.