Both are relly great for pop music. But on the same level as say Mozart or Beethovan?
Nope. But both are amazing musicians.
Beethoven is more accessible...but audience taste differs these days compared to his time. Posterity's tastes regarding Beethoven is a bit different than his contemporaries. The Septet was Beethoven's calling card and moneymaker while he was alive. That made Beethoven apparently hate the Septet. So Beethoven did have his "pop" or "easy listening" work in his early career.
He also wrote his love songs too.
A now-forgotten Beethoven work is his Andante favori. The originally intended 2nd movement of the Waldstein, and the opening is bascially calling out the name of someone he was in love with (Josephina).
https://en.wikipedia.org/wiki/Josephine_Brunsvik
Another is "Ich Denke Dein". There is the song itself and the themes and variation for duet.
Few hundred years later, he's now old and mostly preserved by a bunch of isolationists with some head-in-the-clouds attitude about music. Lot of focus on the symphonies, and the ways to interpret them. This probably leads people to view Beethoven as some monk or otherworldly figure. In actuality, some of his outpurings are quite "real". Dealing with the mental anguish of becoming deaf. Falling in love with someone but being unable to be together. Beethoven wrote love songs. Love songs may be common, but a master can still hit you in the feels with one; I know the variations for Ich Denke Dein do for me. Break ups can be the grounds for a hit(Taylor Swift sure made good use of that).
Elton John isn't writing a symphony, but one could try to size up his songs with some of the "songs" Beethoven wrote and see if they in terms of emotional effectiveness and creative key changes.
Mozart is well-respected, but comprehending him is a taller order for him compared to Beethoven or Bach. It's not the style Mozart wrote for that made him a genius. It's more on the nuts and bolts level, in which he leaves people wondering how he did so much with such a seemingly simple, not overly complicated score.
I wouldn't put Elton John with Mozart, but John does have a rather advanced level of musical ability that could be argued as genius.