Ill tell you a secret. It's not the only site that makes statistics for titles/mounts.
GuildOx is very inaccurate and has always been. Deal with it.
My digging around is oke I guess. Wild Gladiator got obtained by 150 players in EU and probably around 100-120 in US.
Original Scarab Lords, there were probably around 200-220 realms EU and US. (EU had less cause WoW got released in 2005 here) Each of these realm usually had 1 SL, possibly 2.
http://www.arenamate.net/arena-rbg-title-cutoffs.
Your doing simplistic thinking tbh. But it's alright if you think Groundbreaker is the rarest.
You are however right, in saying that when you all sum the R1's all together is probably around 0.1 or 0.2% rarity.
It's the same kind of title each season, with only a different name.