Ive been thinking about this for a long time, and the more i think on it, the more i think it does need to be stated.
Raid attackers and gym attackers arent always the same. Look at machamp, it cuts through the uber tank normal types like butter, but when it comes to raids, most of the big target legendaries (mewtwo, lugia, the birds, Rayquaza, etc) its garbage against, only really coming into use as a raid attacker to get the good legendry's counters (note i said "good" legendaries, not the regi's) ie, Tyranitar. (Houndooms just an inferior tyranitar, and absol, theres research tasks) Serving only an indirect use that isnt required unless going for 2-3 man takedowns
On the other side, theres pokemon that are great for raid offense, but not all that great for reliable gym offense, like gengar, shadow ball mewtwo, gardevoir, some Rhydon sets, pokemon whose offense and in some lack of bulk, is more suited for taking down raids faster rather then be healed up for every gym battle
And yes, there are pokemon that excel at both, Tyrantiar, Dragonite, assorted legendaries, but more often than not, a pokemon's use is either raids OR gyms, and having a rating system for just offense in general can mislead the usefulness of many pokemon