Untouchable - does this set act like block debuffs - it does not actually give protection against attacks?

Also - I have a nuker team which does well but sometimes I hit a team that looks like I should take it out and even after serris has stripped they seem to resist my nuke - is it likely they are built with high def, or resistance or have a gear set like guardian or lethal?

I know it may not be that easy but any help appreciated thanks