My indecision on this (one of my favorite things about this game is pondering decisions to death) may have led me to a whole other solution.
I took a Triangles character on a bit of a trial run – a replay of an old mission. Not very satisfactory, in large part because of a weird bug: the game repeatedly failed to give +1 attack simultaneously for the Soothsinger’s Power Ballad song and the Elementalist’s Formless Power bonus. However, I realized that in this one mission, I had taken the Triangles character more than halfway to retirement, and that it would be trivial to get him to retirement in one more go. And this would open up the Lightning class, which I found to be very good in Guildmaster mode. And since it can soak up some damage, I think that that is probably the way I will go.
I do like playing the Spellweaver, but I seem not to have the knack for doing it right. To my eye, a low level Sellweaver has to burn cards – she has so few non-burn attacks that I quickly have to resort to burn attacks or else burn a card retrieving other cards through a rest. And of course Reviving Ether only works once. I probably have my deck set up poorly or else I am missing some strategy… On the other hand, her retirement goal involves exhausting, so I could just take her along for a while and let it happen. She certainly provides amazing firepower as long as she lasts.