Headphones might need to be run in

It’s not completely proven, but it does seem probable that headphones benefit from wearing in to some extent. Something around 40-hours of normal usage would seem to be the magic number. The RHA MA750i pair that I’ve just bought apparently need more running in than most.

iOS has a ‘late-night’ mode that makes a huge difference in noisy environments

Under Settings > Music > EQ, there’s a Late Night option which compresses audio into a smaller range which makes it sound better in a noisy environment like a plane, office or streetscape. Unlike the other EQ settings, this mode affects all audio output from the phone, including video and app audio.

iOS EQ only affects the music app

Spotify audio is unaffected by the iOS EQ setting. But Spotify has its own EQ setting under Settings > Playback > EQ.