Both Grass and Metal has had decent, if not strong, energy accelerants in the form of Metal Links Bronzong, Magnetic Circuit Magnezone, Voltage Beat Rillaboom (and Strong Charge Vikavolt), etc. Currently they have Giga Magnet Magnezone and Spring Bloom Cherrim too, though definitely not as impactful as Baxcalibur right now.
The types has phases where it goes up and down in the bar of energy acceleration, but Fighting is the only one that has been stuck at the bottom.
edit: On that note, I strongly believe they cant print a Metal Rain Dance as long as Dialga VStar is in rotation. God knows the horror it can conjure...