Not necessarily, plenty of full sus bikes come into the sub £1k category these days that are decent enough bikes. And 16 stone is not light, but mountain bikes are built to take abuse from big heavy people too.
I would still say that sub £1k a hardtail will represent better value for money, and overall performance though.
If he’s looking in Evans, I can’t recommend Genesis Bikes highly enough. I’ve got an Altitude frame which I built up into a custom bike, but there’s plenty of off the shelf options. The Altitude 10 is £949 iirc and recently won a sub £1k shootout in MBUK magazine. I love mine, perhaps I’m biased, but I don’t think there’s many all round packages out there better for the money. Sure, you can buy hardtails that are lighter, or come with flashier kit, but as an allround package the Altitude is a great bike.