So I was looking through some legendary discographies and I cam across a few that really tripped me out. Elton John's Tiny Dancer only peaked at number 41 but it's clearly his signature song and still played a lot today. Another is Oasis Champagne Supernova which did okay in the U.S. at number 20 but didn't even chart in their hometown the UK. What other instances has this happened? Also does this discredit what peak positions are since this site seems to think just because a song isn't an immediate smash it can grow bigger over time?

A song's popularity relative to others in that exact moment. It doesn't speak to popularity over a longer period at all.

In all honesty they're kind of misleading. Sales and longevity matter a whole lot more than a song's peak position. For example:

Marry You by Bruno Mars peaked at #85 and is 2x platinum in the US alone
Cheerleader peaked at #1 and is at like 1.6 million in the US

Exactly I bet any money that Marry You will be one of Bruno's most remembered songs.

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They show how popular a song is, but the chart run is important too

What other songs are more prominent now than at the time?

I feel like a lot of Lana Del Rey songs will be bigger in 20 years than they are now.