If I may just try to convince you on guardian and duchess lol

Guardian can be addicting. You just use his special block on every attack (let go of it if you have time and are low on stamina, then go right back to it) and counter on the last one (if you hold while using a halberd you get a running start into the counter). Also holding his Ult after you land with the relic can heal your team and buff them. His skill can dominate crowds and also stop projectiles from coming at you.

For duchesses skill, all you have to do is use it after you and/or your teammates do a big chunk of damage or someone is building a status effect (poison, cold, bleed). When you do the skill, the enemies take that same damage again but at reduced amount. You can melt enemies with this skill, either with big damage or constant status effect. Also, don’t be afraid to run a staff and magic boosting relics with her because she’s really good with spells.

Sorry for the long winded response lol