That can't actually account for perceived loudness, which modern mastering processes
do account for. The absolute amplitude of a song has always been fixed, by the technology delivering the audio. Radio, the primary medium for music discovery throughout most of our lives, has a very hard upper bound (set by both the technology and the FCC), thus a compressor/limiter is employed at the final stage before sending the audio out of the radio station to go up the tower and out over the waves. There has always been
that sort of leveling going on.
Modern tools provide an entirely new dimension in the form of multi-band compression, digital phase alignment, etc. It is now possible (and being done in nearly every genre) to make a recording perceptively louder than other recordings by maximizing amplitude in specific bands (those humans are most sensitive to), reduce phase cancellation between speakers, and hype the sound (boosting high and low frequencies, which tricks the ear into hearing it in the same way as louder music...but also causes listener fatigue faster), often all at once.
Amplitude compression, even when it's smart enough to recognize that there's more activity across a broader spectrum as provided by SoundCheck, does nothing to restore the damage to dynamic range, natural frequency response curves, and "real" sounding recorded music. The music is broken by these processes...the listener has no power to fix it, other than to not buy it, and choose music that hasn't been mutilated in such a way.