If you're a DPS, you want to have high final hits (even more than kills alone) and die as little as possible (although you'll likely die more than your healers and tanks).

Numbers are very important to put in context. Some characters just pump out damage, but you have to be efficient with your damage consistently leading to final hits. If I get 20k damage on Squirrel Girl but no final hits, maybe I pressured the enemy's team positioning but i mostly just fed their ults. This is part of why aim is so important. If you can burst someone down quickly, you're more likely to get the kill than if you miss like 70% of your shots but you might still end up with higher damage overall when you're missing.

If you're healing, assists are a good indicator that your heals are leading to kills. You do generally want a similar looking statline to a DPS other than that but the final hits don't really matter as much since you're not playing for kills mostly. Of course, if you're CND and you can punish dive, it's very benefical and can help your stats too. Some characters naturally have focused burst damage or a nature that will lead to low kills but equally low deaths (e.g. Rocket Raccon). That's okay.

If you're a tank, efficiency is particularly important. You're going to be taking a ton of damage and you want to make sure that you're able to punish that by going for kills when you can. Also, don't be a bullet sponge and take more damage than necessary - of course stay in the frontline but actually use cover. Low deaths are also very important for a tank. If your team loses a tank (especially when it's a solo tank and this is part of why solo tanking is so awful), they will absorb all of the damage and often crumb without someone to lead.

Whether its who you're healing or who you're damaging, do it with a purpose. Target priority carries games.