Would this be a form of abuse or just bad parenting?

This is actually worse ABUSE towards the younger sibling if you believe it, for it made the older one doubt himself and think he is unworthy (but that can make some one want to prove his worth even more which could be helpful, BUT it could back fire), but for the younger one it distorts his entire world view, the one in which he is always right, backed up, untouchable (it could turn into a sort of god complex WHICH IS THE WORST CASE POSSIBLE so do not worry), and never punished for putting his older brother (which he should respect and adore) through hell which can make him despise authority for the way his mother used it re-live her high school life in which (most likely) she was picked on and bullied (usually the parent sides with the better looking child) and making him not appreciate/respect elders the way he should.