1) The Sixth Sense was an enormously popular film, so clearly ‘cheap suspense’ (the final twist) is attractive to a lot ofaudiences. We already know this from Agatha Christie novels, which also speciliase in the crucial last minute reveal. No professional writer ignores massive audience approval.
2) The final twist is, I would suggest, usually well-planned. It is certainly not easy, as the term ‘cheap’ suggests. To mislead the audience so that the majority never pick the final twist is very clever indeed.
What fascinates me that a value judgement on a narrative structure is being passed off as valid criticism. Suspense cannot be ‘cheap’. Suspense is suspense until it’s proven to have been unmerited. You can criticise a film that sets up great suspense then doesn’t pay it off. Fine. But moral judgements? I don’t think so.