You're assuming that the reason people who aren't seen are more likely to be awarded, than those who are seen, is because they managed to fool the assessors better by not being present.
But from both personal experience and being generally informed, I would say that the reason is it's easier for assessors to miss, ignore, or fail to fully identify (whether accidentally or deliberately) the claimant's issues in person.
Therefore the "true" claim rate is closer to the unseen applicants. Even then though, it's very common for it to be initially refused and then overturned at MR or appeal stage. I.e. the successful claim rate should actually be higher than it is, not lower. Unless you just want to save money, or hate disabled people. Is one of those your motive for wanting this change?
My disability means that I would not get a fair assessment in person, so yes, I would be one of those people who might lose it. But not because I don't meet the criteria. The first time I applied (both my claims were assessed not in person), it was refused (and then awarded at MR). At renewal, it was awarded for 10 years (which is the max).
For my daughter, I had to go through three tribunals to get DLA awarded.
If you'd experienced this exhausting, dehumanising process yourself (and don't forget that disability benefits are supposed to be making life easier for us, not the opposite!), maybe you'd be less keen to withhold them from others (though sometimes the opposite is true, and people pull up the drawbridge behind them, out of fear).