If an insurance company screws up and loses money on what it thought was a low-risk investment, is it still obligated to pay out your beneficiaries?

Sure, but if it screws up in a sufficiently epic fashion it won't have any money to pay to your beneficiaries.

Do you believe you are less likely to screw up in this manner than a professional fund manager hired by a multi-million dollar company whose existence depends on accurate forecasts?

Me? Why, yes, I do.

Will your heirs and/or creditors find it easier to grab your portfolio or an insurance policy of which they are neither the owners nor the beneficiaries?

I don't know enough of bankruptcy/probate law to answer.

I might also point out that I had said nothing about the wisdom of buying term life insurance. I suspect that, as usual, it depends. For some people it's a good deal, for others not so much.