RG grads don't have "greater opportunities" than those going to non RG unis in general. The RG is a pretty broad range of unis and while some may have specific advantages in particular fields (e.g. Oxbridge, LSE, UCL, Warwick and Imperial for investment banking) plenty won't make any difference in any field or may even be worse than others in particular fields/areas.
e.g. SOAS commands a much greater level of prestige internationally in countries speaking languages it teaches as it's well known outside of the UK; within the UK Bath and St Andrews are much better known than some RG unis and Bath particularly has very good track records in graduate placements. Other unis like Loughborough, Strathclyde, and Heriot-Watt place graduates very well within areas they are well known (mainly engineering and related areas).