Technically, an issue with lossy formats is if they get saved, moved, and/or re-encoded then there is a risk of media degrading over time, over iterations. So you could potentially hear the difference.
But FLAC is lossless.
If the user likes the MP3 sound better then clearly they actually enjoy the lossy hum and buzz of compressed audio. I'm sure they would enjoy Vinyl.
What.cd was the greatest collection of obscure music the planet has probably ever seen. I dont even particularly care about lossless codecs, I was fine with 320kb/s mp3 as it was more convenient but even their mp3 rips were way better than other places, and you knew everything would be tagged and sorted correctly. And they had EVERYTHING you could think of, it was wild.
Yeah, I am still doing everything I can to keep my collection backed up on external HDDs (probably should upload it somewhere). Not only obscure stuff, but incredible vinyl (and in some cases Reel-to-Reel) rips of classic albums.
And yes, you absolutely could tell the difference.
I would usually get v0, but would sometimes pick up FLAC, especially if it was one of the staff recs where you'd get upload credits but no download hit... Pumped that ratio up.