I personally find this unnecessary because most of it is pretty much covered here: http://harem-battle.club/millennium-...-1-2015-a.html
just that it might be a little long if you read all, which I reckon is why most newbies just go tl;dr (I mean, I doubt newbies will understand everything there until they actually experience the class and units for themselves)

also, ALL (except the occasional exceptions, if any) ranged enemies actually attack the order of last unit placed. It is merely commonly referred to as 'Lich aggro rules' because Lich is the first enemy that we encountered difficulty in managing its targeting due to its high damage and insane range.

Also, although you say 'strength and weakness', strengths can be weaknesses under certain situations, and vice versa (valkyrie's 1 block is both a weakness and a strength. I would NOT want a valk to block more than 1 in the current DMM event, seriously. 700 damage from the black tiger is scary enough, no need to upgrade it to 700 x2)