Plagiarism is more reserved for directly copying the original thought of others.
Copying thought of others is allowed only if a source link is used or it is put in a quote block. Without a quote block, a source link, it is plagiarism.
The ban is lenient and becomes more lenient last two years and community already question moderators about that. No official answer but in the past, if a plagiarism is made to earn money, to meet campaign post quota, it will cause a permanent ban. It is no longer true last two years and nowadays it seems shit posters are banned by AI-content more than by plagiarsim.
Plagiarism is what gets people permabanned, not just copying. Plagiarism is copying with the intent of passing the work off as your own. In essentially all cases, plagiarism deserves a permaban because it usually proves definitively that the person is here for the wrong reasons: to fill up space in order to get paid, not to actually discuss or contribute. If someone was able to convince us that they were plagiarizing just to eg. impress people rather than to fill up space, then a lesser ban of a few months might instead be warranted. But this has never happened AFAICR. (Arguments based on plausible deniability aren't going to work; we don't need to prove that you had the motive we see in your actions.)