Hello SG. I have an idea. I think maybe SG can come up with Class Summon which summons only a specific class of heroes. Normal payments of gems for a single pull and 10 pulls. Basically, when you summon class of Ranger, you will only get a Ranger hero 3 to 5 star and of course the HOTM is a possibility too and the Class Summon alternates with Elemental Summon. That way, we can use gems for those specific Class.
If it comes together with Trial quest, then two classes of heroes are in the pot. Meaning that, if the trials quest is for Sorcerers and Wizards, then the Class Summon consists of Sorcerers and Wizards Heroes only.