Niv-Mizzet, Parun is the textbook commander for this style: you control the early turns with counters and removal, then use those spells to protect Niv during a Curiosity combo finish
You want cards that work as mass artifact destruction as cheaply as possible, so Farewell usually wont do it at 6 mana
Plus, you can add in unblockable infrastructure you likely already have in the deck to win
A commander like Muldrotha, the GravetideMuldrotha, the Gravetide might want more ways to mill cardsmill cards than to draw them
normally it costs six generic and two red mana to cast, but the generic mana needed to cast it is lowered by one for each Instant and Sorcery card in the caster's graveyard
Theres a whole bunch of cool cards beyond Esper Sentinel, Land Tax and Silence that should find their way into your decks, especially when youre looking to steer away from running the same few cards over and over