Could it be that these cards are cheaper and cheaper cards perform better in bo1? (Do they?) And is it even a statistically significant pattern?

Unscrupulous Agent (MKM) P: 2nd T: 2nd
Skullcap Snail (LCI) P: 9th T: 9th
Nezumi Informant (MOM) P: 3rd T: 5th
Corrupt Court Official (SNC) P: 4th T: 4th
Virus Beetle (NEO) P: 2nd T: 3rd
Elderfang Disciple (KHM) P: 3rd T: 3rd

I wonder if this is because bo3 has more opening hands with 4/5 lands?

True. Then I'm convinced going for lethal is bad. Relic activation line wins more often.

I guess if you're not required to manually tap for Relic (i.e. autotapper leaves up Island), they could sloppily not respond to it

if they have something, then I think Elspeth lives - they kill Boulderborn in response to Relic or in begin combat if you attack first

I kinda like play Naga, decline to copy, renew on Dragon attack for 23.