There is no rule text stating that these activations don't stack
Sure, it might only be during combat, but when paired with your Amulet, this can make you an instant-speed untapped blocker
Legendary Land Oswald Fiddlebender Magical Tinkering , , Sacrifice an artifact: Search your library for an artifact card with mana value equal to 1 plus the sacrificed artifact's mana value, put it onto the battlefield, then shuffle
Channel and Sneak Attack don't have similar rules text, for example, but they overlap in their ability to do broken things with big colorless creatures, so you might pick up a Sneak Attack to support your early-pick Channel, and then prioritize the legendary Eldrazi creatures, Blightsteel Colossus, and Sundering Titan over a card like Karn Liberated, which only works with the Channel plan