I think the issue of deciding who gets an offer - whether it be through A level cut off, degree cut off, grade weighting, psychometric tests, etc - is that there are just so many people applying to these firms, and they don't have the manpower, time or expense to make in-depth decisions. MC firms have around 3000 people applying for a vac scheme - and would have more but for the cutoff. It will take far, far too long to go through each and every one of those applications purely on the virtue of the competency answers on the form and not considering anything else. It isn't time-efficient, and especially at graduate entry level, trainees are cannon fodder and are fairly easily replaceable, so the grade focus is a good way at least initially of slimming down the applicant numbers.
Grade requirements are no worse a way than any other of doing this, for two reasons in particular:
- If you read law at university but performed very poorly in certain important modules like contract, the firm might have good reason to be concerned why you did so badly in an area of law so important to their work.
- One of the most important - and necessary - qualities in any commercial lawyer is the ability to handle hard work, and a lot of it, mixed in with competing deadlines. If you weren't able to handle this at university/school, that could be a warning sign that you might find it difficult to handle a commercial lawyer's workload/life.
Naturally, some people have extenuating circumstances, and that's why firms take this into account if you explain this to them. On top of that, if you went to a private school with an amazing teacher/pupil ratio & low levels of class misbehaviour, then you'd have likely stood a better chance of doing well at A level - so again, this method definitely isn't perfect, but works decently.
What are the alternatives to this? Well, psychometric tests such as Watson Glaser are an alternative - and many firms use these anyway - but these too have their shortcomings. The first and most obvious problem is that you can game the Watson Glaser test. It only has so many questions to choose from, and after a while of practicing it, you've seen all the questions and know how to answer. The second problem is that some people naturally are very good at psychometric tests, and some really aren't. Yes, you can get better through practice, but some people still have that advantage, so these tests aren't some sort of great leveler where everyone has an equally good chance.
Other than that, how else can you decide? You could do it on extra-curriculars - but even then, too many people do them. You run a law blog? Great, so do 500 other people. You were on the committee of your university law society? Cool, never heard that one before. Extra-curriculars add value to your application, but you can't just decide on them alone.
It's also worth noting that at least some firms do consider the university you read your subject at, not just the degree result itself (confirmed to me by a partner from a top firm, whom I met in a social situation). That's because a lot of non-RG universities (and some RG universities) hand out firsts like confetti, which therefore places candidates from universities with more stringent awarding requirements at a disadvantage.
As Jessica & Jaysen have said so often on the forum, less than stellar grades aren't an automatic bar from commercial law, they just make it a bit more difficult - particularly in applying to firms like S&M, S&S and so on. If the rest of your application, your extra-curriculars, your competencies, your commercial awareness & your Watson Glaser scores are good, they will more than compensate for the bad grades in most cases.