The phono preamps used in most name brand receivers these days are perfectly good and although I can't say I've seen carefully prepared measurements on all
of them what I can say is that all that I have seen are excellent to stellar
in regards to frequency response error into typical, standardized MM cartridge loads and often outdo their published specs.
Unfortunately finding measurements on them in 2019, decades after LP's heyday, is difficult, but what I have found to show as an example is the frequency response of an inexpensive stand alone phono preamp showing that "outstanding performance" is dirt cheap these days. Here is Stereophile's measurements of a $199 NAD phono preamp which according to NAD uses an identical circuit to their $129 stand alone unit called the PP2 [a simpler unit without extra digital features]. I wouldn't be surprised if it is exactly
what they use in their receivers, integrated amps, and preamps with phono stages:
[left channel blue, right red]
As you can see, between the 20-20kHz standard range it is very, very
flat, deviating only within a very narrow window of perhaps .25 or .3dB. To the ear this deviation would be inaudible to everyone.
Other brands may not be quite as good as this but even double this amount of error would still be inaudible.