You can only roll with 30 quartz you bought (the bonus quartz that you get when buying doesn't count so you have to at least buy 25+4+1 if you don't have any paid quartz) and you roll one of the two gachas depending on which class you want (Saber/Lancer/Archer/Ruler/Avenger or Rider/Caster/Assassin/Berserker, I think) and you get a 5* of one of those classes guaranteed.
To add to that Lancelot still deals half damage to archers, and Artoria's NP gives her invulnerability/evasion pierce for her entire turn including her AOE NP.
I prefer my motto: "If there's something you need to do, but you're nervous/worried/afraid of it, just don't do it, and hope everything works out on its own or someone else does it for you"
Yeah, and it's great that they do... but a battle where you and the boss smack each other about with wet noodles for less than 1000 damage at a time is dull as shit.
DW really knows how to make interesting and tense battles. A saber that takes and deals resist damage to archers? That's not going to take 10 million years