TLDR: Maybe, depending on your roster. He's fairly reliant on Embryo Fusion generators/Aliemus batteries such as Thais, Horla, Winkle, etc. to feel usable. E2 is the minimum investment level to not feel outclassed by competitors. If you lack Thais and don't have enough pulls for at least E2 (and ideally more), you may want to consider against pulling him unless you're desperate for a Caro DPS (although you could just use Uvhash at that point if you're that desperate for bodies).
Doresain is a Caro Attacker who focuses on dealing massive single target damage. His own action economy is generally quite low and (unlike his competitors) he doesn't actively drain your own life to do damage (only 1 card uses health, and considering how hard Caro prints Vulnerable onto the enemy it's probably not worth even using). This gives him a very specific niche compared to the traditionally higher risk Caro DPS options. With that said, much of his damage is heavily reliant on his Exalt, requiring you to either build a full Caro team that can consistently generate Embryos OR pair him with multiple Aliemus generator supports from other realms. Pure Caro struggles to field more than 1 full team (with the extremely contested Thais being monopolized by other Caro DPS, particularly GHelot) and mixed realm teams force you to sacrifice pivotal members from other teams to be worth using (Horla + Winkle, Miryam, technically Doll/G-Doll).
If you already own an invested G-Helot, there's really not much reason to pull him for meta reasons. There are other DPS options in other realms that can cover D-Tide, and his single target focus at low dupes means he isn't a plug and play option for all content. He certainly does feel quite good from my testing, and his damage output is quite respectable even at low investment, but both G-Helot and (to a lesser extent) Uvhash are capable of outputting massive damage as well.
With that said, Doresain's single target damage output is genuinely VERY good. His ultimate can easily hit for 5-6 digits with shockingly little ramp up time and he's a significantly safer Caro DPS to use. With dupe investment Doresain's value also greatly increases. E2 is a decent damage boost, but E3 immediately fixes his AOE issues and lets him clear most exploration stages with impunity. It's also just a really good card to hold on to for nuking bosses (I can regularly get 6-7 copies of them against high difficulty D-Tide bosses, which when scaled up can easily one turn a boss alongside his exalt). Overexalt introduces a significant jump to his damage output when fully stocked on corpses (though Aliemus generation can be a limiting factor). Still, this level of investment is probably outside the realm of the average player, so consider whether it's worth investing that many pulls into a character in lieu of future characters.
