Equivalent time sampling scopes don't have the same trouble with aliasing provided the signal you are observing is repetitive.
That is true but DSOs that support equivalent time sampling usually do not at slower sweep speeds (1) where the real time sample rate will completely fill the acquisition record in one acquisition and many DSOs back then did not support equivalent time sampling at all. For a while it was a premium feature.
So detecting possible aliasing by comparing the processed trigger and sample rate would still be useful even on a DSO which supports equivalent time sampling. It would be useful even with the huge record lengths available today.
Unfortunately Tek has dropped this feature on its newer scopes in favour of interpolation with all the issues of aliasing. It's a pity because they did it extremely well on the scopes that offered it.
Most manufacturers dropped it and the reason is simple enough; the performance of integrated ADCs and memory reached a point where real time sampling rates were sufficient to support digital triggering at a cost lower than the dedicated hardware needed to measure the trigger to sampling clock delay for equivalent time sampling.
Support for equivalent time sampling is still found in higher end DSOs were the cost of supporting a real time sample rate high enough for increased bandwidth is prohibitive.
(1) DPO style DSOs do not care a whit about this. They effectively always operate in equivalent time mode.