Oh yes, absolutely. This particular scheme is very heavily pre-funded (currently to ~30% of salary, which is why many employers want it dead) and is sustainable as long as your investment strategy isn't 'putting the money under the mattress'. Yes, residual investment risk falls on the universities collectively (by deliberate scheme design) but it's certainly not one of the over-promised schemes of the kind you note. In fact, it's status as a nominally private-sector scheme subjects it to heavy regulation specifically to ensure that the government doesn't get left holding the bag.
If you want far more detail than is sane, there was a 'Joint Expert Panel' set up by the employers organisation and the union to provide a way forward after the industrial action caused by the last attempt to abolish the scheme. Their report analyses USS in detail (rather than pension schemes in general) and is at https://web.archive.org/web/20220506092908/https://ussjep.or...