There are a couple of crucial points I’ve noticed.
1/ Most top players with deep roster seem to be able to beat this team frequently (well I don’t know how close the fight was 'cause there’s no record), but for average-tier players who stack colors and depend on luck, the board just needs to be a bit unfavorable to make them really struggle.
2/ I watched a lot of Zero’s raid videos, his win/lose ratio appear to be pretty similar (well just based on the raid history he showed). Considering his level of invincibility, I don’t think others with similar defense - Guin tank - are doing any better plus most Zero’s troops are mana and maxed).
3/ I put Elena and Tarlak at the corners not because of their special skill but because of their attack punch (800+). Crit troops give them chance of crit hits. This may play an important role. It’s only a guess though 'cause as I said, video records of enemy’s raids are not available.