Another layer to this is monsters typically aren't given the strongest spells more often than not they're given underperforming spells and then become a problem when those spells are buffed to on par with existing options, like BDB and Melf's acid arrow being the current example.
Enervation largely became a problem when it got buffed to contain a dot but until then we didn't even know how many enemies actually used it, until then player characters basically never cast it.
Until Black Dragon Bolt got buffed it was so negligible that players never used it over other options and it was so weak we hardly noticed enemies used it except for when we were trying to open doors after the caster was dead.
Undertuned spells being made viable for us and overpowered in the hands of monsters is a recurring problem. In fact I recognise that I myself complain Sunburst is undertuned for its level and Light as a spell category suffers for it but at the same time I dread it being buffed because it's so bad it has constantly been given to monsters and traps.