I believe siege elephant of india is really bad vs organ gun and gatlings. Because they overkill. One weakness of gatling compared to falc is they are less tanky. They die in 1 culv shot. Falconet dies in 2. However, for siege elephant they still need 2 shots to kill. The second shot overkills so much. So gatling gun is as tanky as falcs for india. So vs european 2 falc shipment, siege ele and culvs need 4 shots to clear. Vs USA 3 gatling, culvs need 3 shots, siege elephants need 6 shots. Combined with shorter range of siege elephant and increases multiplier skirms have against siege eles, it is very difficult to land 6 shots without losing the elephant (against a decent player), USA has sharpshooters.
Falc hp : 200
Culv damage per shot: 160
Gatling hp: 150
Siege elephant damage: 100
Same applies to Portuguese organ guns, and Portuguese has faster moving skirms. It is very hard to kill cannons without losing the siege elephant.
So gatling hp is between 1 siege ele shot and 1 culv shot. Is this intentional design choice or just happens randomly?