Never had an issue with spellcaster scaling until today. A player in the group claims he can cast Eldrich Blast twice on his turn. Once as an action, and a second time as a bonus action since it is a cantrip. Allowing him to shoot 4 beams for a d10 each (he's 5th level so 2 beams per cast). This seems vastly stronger than anyone else's max 2 attacks. After the session which ended early with many players angry this player ruined all encounters, there was much talk of re-rolling into all caster party. One wanting to do the same with a wizards Firebolt spell as a bonus every turn, others still browsing.
So, is it possible for a caster to cast multiple spells in 1 turn? From what I was quoted from the PHB, it's possible to cast any spell as an action, then cast a second spell; as long as the bonus action spell was a cantrip with a cast time of 1 action? So 99% of all cantrips? Please tell me this is wrong, because I feel that if anyone else does this our melee characters will never see a fight again before the casters nuke them down.