The personal statement is also really important for students who aren't meeting the grade requirements.
No, it isn't. Or at least, not at the time of applications, for the vast majority of courses. That goes double for 18/19 year old at the point of admission home students applying with A Levels or IB.
Outside a handful of low-numbers courses with tricky requirements, large universities do not read personal statements other than in exceptional cases. It is possible the personal statement might be read prior to a offer-holder day if they offer a one-to-one, but by then an offer has been made. The personal statement is more likely be read on results day in the event of a decision over which candidates who have missed their grades should be admitted or whether clearing would be better. But even then the decision is much more likely to be made on the basis of which grades were missed or which non-compulsory but desirable A Levels were taken.
There are some subjects where personal statements are said to matter: medicine. There are some universities which are said to more use them as part of making offers: usually, unsurprisingly, the boutique ones criticised on MN for being late making decisions, like Exeter or St Andrews. I presume that universities which interview but do not ask for additional material use personal statements, such as Imperial, use them, but I don't know.
But in large universities, all home and most international admissions are done centrally up to the point of decisions on results day. The administrators have very little discretion, and basically make offers to everyone whose predicted grades and supporting GCSEs meet certain criteria.
A popular course at a large university will have 1000+ applications per year, most of them fairly plausible. Do people seriously believe that 1000 personal statements are read?
Someone who applies for five courses substantially outside their predicted grades is taking a risk. If those applications are to big courses at big universities, then there is a substantial risk they will receive no offers. They might be lucky and get offers although, in general, schools are generous with predictions (too generous, often) and even once they have an offer above their predictions they still need to make the offer. If they are prepared to risk either a gap year or getting involving in the rather murky waters of continuing application or de novo applications in clearing, then fine. But they should be clear-eyed about the risk they are taking.
Personally, now I work inside the system, if my children had not already started university I would advise doing nothing about university until after they have their A Level results. The UCAS system is opaque, and the more I know about it from inside the more arbitrary I think its outcomes sometimes are. An application in September with your A Levels in your hand is transparent and obvious. Conditional offers are more complex.