And because it’s so much fun, some more data :-)
Who has played the most BM4 games? That would be our beloved @simon33 who unfortunately went AWOL a couple of weeks ago.

You can see clearly how he improved a lot, from his lowest point in March 2017 (1077 ELO) to his highest Rating in May 2019 (1693 ELO). Which is to be expected!
Now from then on his rating gradually declined - slowly but steady. Did he become worse? Maybe.
But remember, we are not measuring an absolute value. Your ELO rating is actually only a number that gives you a relation to the other players. So it’s not absolute, it’s relative to every other player.
I’d interpret this graph differently: I think over the past ~4 years his skill level plateaued or stagnated but A) more and more other people did improve while he did not and B) more and more new people joined the league who are on average better than him.
And now a completely different graph. The player with the 3rd most completed BM4-games, after @simon33 and @Giallo ?
Our very own @axis-dominion
Here is your graph, Mister:

A steady climb at the beginning where he chose mostly average players and won consistently almost all of those games.
The opponents were weaker than him, but still reasonably close so the games were still worth something. The climb could have been a lot faster had he won against the top players from the get go - but he didn’t! The matches against already strong Adam514 back then were almost all losses.
An unbelievable streak of 30 wins in 31 games between July 18 and March 19 (the only loss was against, of course, Adam514) rewarded him his all-time high of 2101.
3 losses on 16 Apr 2019 (probably mass forfeit?) saw him drop a whopping 158 points before his break.
A steady climb after his return brought him back to the top, although his rating seems to have plateaued around 2030