You may discover that limiting yourself by one color opens the door to some of the most exciting Commander decks you'll ever build.
Red Shanks Yellow Kalgara Purple Sengoku Black Crocodile Blue Buggy Green Dracule Mihawk Green Dracule Mihawk gains a +1,000 Power boost if youre against a attribute Leader, so if youre going up against a deck like Green Zoro, youre gaining a massive advantage throughout the whole game
I can understand why Wizards printed it at mythic the first time around they wanted to make sure that they didnt crash the price of the card and create a situation similar to Chronicles
Its not like Thoughtseize is ever dead
It's not exactly easily accessible given its playability in Modern and other Eternal formats
You can also use Karn, the Great Creator to look beyond your deck for combo pieces (which could include things like Rings of Brighthearth, Lithoform Engine, Spike of Ish Sah, or more)