The pension may be held in trust, but if the employer goes under, the pension stops getting new contributions. In many cases, this led to insolvency of the fund as well, since contributions before employer insolvency were usually not high enough to ensure fund assets could cover future obligations.
>>kbolin+(OP)
Indeed. A proper fund should be a managed investment fund like the Canadian Pension Plan fund for example.
I do not think a fund is better than a 401k in terms of returns over investment. But it's for sure easier for the employee, as retirement fund is a complex topic better managed by professionals.