And what's wrong with evolving in the middle of the league? We've had plenty of league evolutions in the past before“Made sense” =/= feeling good, well-earned or needed.
There was no special thing which prompted Meltan to send signals to its fellow Meltan. The writers just felt it was convenient in the middle of the league.
Ash’s capture and evolution of Meltan will always feel unneeded and meh to me.