I reckon a good rule of thumb for the "overratedness" of a university, not so much in terms of how the university rates itself but how its own students and alumni overrate it, is how much its students and alumni have to engage in constant arguments to 'prove' that their institution is in fact great, showing league tables or some other stat that puts them on par with institutions which are generally regarded as above it, or showing that they are higher than others that might be considered as 'rivals' in the same league.
You never see Harvard grads trailing round the internets wanting to prove to everybody that Harvard is better than other institutions. You don't even really see the Oxbridge grads on here going round feeling the need to 'prove' Oxbridge's superiority to Leicester or Hull etc.
The SOAS haters are a good example. Whenever you see someone, at one of the London institutions, going on about "well my institution IS better than SOAS!" as evidence of how good their university is....seriously nobody outside of the University of London cares! But you see this a disproportionate amount of time on the internet, especially from students at UCL or KCL, they always want to tell you that their institution is better than SOAS lol.