That depends how you define content.
I have done a little bit of research on past content removeal since 2003. The only time CCP took away a whole gameplay activity was back in 2012 when they removed the static DED 1 and 2 sites. And there they gave decent reasons for(botting and afk farming), which CCP did not really do with the old provings. There they listed problems which affect other parts of EVE too, especially the “solved meta”.
2016 there was the ban of gambling sites, but these were never introduced by CCP, all player made, so that does not count.
So that means that the removeal of the old proving ground is something completely different than the removeal of the static DED sites. (fun fact: back then the idea of a “proving ground” like the old one came up).
But I can say and most likely confirm: The removeal of the old proving ground feature was the first time in the entire EVE history where CCP directly removed an ingame activity as a whole, without giving an equivalent replace at all.
With the static DED sites, they moved it to the exploration system, so that you have to scan them down. The sites itself remained unchanged. So byebye botting and welcome for those who liked to farm it.
If CCP decided to follow a similar path, they would have either left the old arena alone or gave us a new filament that brings you into the old proving grounds, while these themselves remained unchanged, so still any Cruiser allowed, 1v1, 30 min, 5 min to unlock cache, same scenery etc…
See here: Burner proving grounds as a replacement for the old 1v1 arena at the end of abyssal sites