Ancalagon
Dusty Dragon
The DM can impose whatever restriction they want, and the players can agree with them or not, or perhaps negotiate.Are you allowed to restrict stuff for mechanical reasons? What if the DM thinks artificers are overpowered?
Some of you may familiar with my famous "ladle" system. In the Ladle system there is one race (ladle), one class (ladle), one stat (ladle) and you fight ladle monsters to get ladle coins.
The players have a huge power though - they can tell me "Anc, the ladle system SUCKS and we don't want to play". Ie, VETO.