I guess grades can be a differentiator between equal candidates. But I think less important than psychometric testing, interviews, assessment tasks, application form etc provided you meet the requirements. Obviously somebody who gets 69 average will be more favourable than 61. But if it's a 2:1, it's a 2:1... either way, you can only focus on what you can do in this moment. I won't lie and say that grading is always accurate or fair, but that's out of your control. Fight for every mark, and whatever you get you get. That's all you can do, and no matter what, it will be worthwhile to developing your skills/knowledge and push your grade higher. And developing this mindset will help your career as well.
I got a 2:1 (65) from an RG (but not particularly highly ranked russell group relative to others). I had couple 2:2's, one was barely a 2:2 (nearly 3rd), and both were in relatively important subjects. In fact, probably the most relevent subjects for commercial law. My uni also was very conservative with giving out firsts - I imagine the same with many unis. There were "loosely mitigating" circumstances from lecture strikes, but really my assignments weren't what they were looking for. So far it isn't holding me back, but let's see.