Currently, these two cards mostly see play in Commander, and when looking through EDHRECs usage statistics for these two cards, Guardian Project (139,494 of 1,616,598 eligible decks, or 9%) dwarfs Aurelia (7,660 of 763,421 eligible decks, or 1%) in popularity
Graded Population Report: Chansey [Series 1] #113 Visualize the distrbution of grades in the chart
This allowed us to make three-color commons that played into the shard theme without making cards that were hard to play
Unlike with vendors, these trades are more about utility
Throw Sarulf into a deck box with some +1/+1 counter synergy and you have a great creature deck with an easy way to threaten your opponents if they try to stop you
Able to grab the best card for any situation from your sideboard, if you have a Karn on the field, you're prepared for anything