is non-standard language low-prestige ?

It drpends.  

Given: won baldhaid feller, less cawl him larry....

This is why goofy larry is so anti-wnc-dialect. His UNC book learning was ingrained in his baldhaid that wnc and country folks in general are ignorant because they retained their own langwidges.

Two wit....

https://en.m.wikipedia.org/wiki/Sociolinguistics

"It is generally assumed that non-standard language is low-prestige language. However, in certain groups, such as traditional working-class neighborhoods, standard language may be considered undesirable in many contexts. This is because the working class dialect is generally considered a powerful in-group marker. Historically, humans tend to favor those who look and sound like them, and the use of non-standard varieties (even exaggeratedly so) expresses neighborhood pride and group and class solidarity. There will thus be a considerable difference in use of non-standard varieties when going to the pub or having a neighborhood barbecue compared to going to the bank. One is a relaxed setting, likely with familiar people, and the other has a business aspect to it in which one feels the need to be more professional.

...

Studies, such as those by William Labov in the 1960s, have shown that social aspirations influence speech patterns. This is also true of class aspirations. In the process of wishing to be associated with a certain class (usually the upper class and upper middle class) people who are moving in that direction socio-economically may adjust their speech patterns to sound like them. However, not being native upper-class speakers, they often hypercorrect, which involves overcorrecting their speech to the point of introducing new errors. The same is true for individuals moving down in socio-economic status.

https://en.m.wikipedia.org/wiki/Sociolinguistics