With the addition of Unholy Heat to Modern, not even Lightning Bolt has been able to fully withstand the power creep of the last few years, and I personally would place it below Unholy Heat in power level when taking into consideration the context of the Modern metagame
It may have to attack every turn it can, but in exchange you get an indestructible creature and another source of card draw like Squidward's
The enchantment theme, Rooms, manifest dread, eerie, the return of delirium, impending, glimmers, survival, overlords, and just the whole way it all interacted with a graveyard theme was a huge success, but it was also a lot
It is simply a matter of playing to the complexity that is the game these days
Becoming the Monarch is nice, but there are a lot more Monarch cards with more effective upsides than this one
A 3/4 with vigilance for 4 that also taps for isnt anything to just forget about