To be clear, DD launched 5 hours after WoW Classic launched: Three New Realms Now Open -- 8:20 p.m. PDT August 26
The challenge was that Blizzard did not want to create too many realms at launch (people would complain if this led to many dead servers) but they ended up underestimating demand and were creating new realms on the fly.
True, RP-PvPers already committed to Grob so despite the initial day congestion, not many would flip flop over to DD despite it launching mere hours later.
I play on both Grob and DD and yes, DD is hurting. It would be great if they could connect it to Grob (despite Grob having layers).
That said, since Bliz has left Grob and DD unconnected on Classic Era (and thus killing off those realms), I have no confidence that Blizzard will do anything about this.