Gray's MP before ch499 was clearly below Spriggan's. It would be below Makarov's. This applies for everyone else in the guild sans Laxus and Gildarts imo.
After Gray awakened darkness, I do believe his MP rose. To Spriggan level? Maybe.
As for durability and MP, it's a general rule that MP and durability are positively correlated. Though you can have people on similar MP levels but much different physicals. As @Axiomus said, there are some people who have magic that will assist their physicals. Someone like DiMaria in Chronos form has more durability because of that form. God Serena is a dragon slayer, Wall is a machine - both have better physicals than Neinhart despite their similar MP level.
My initial impression was that Spriggans should have durability at least as good as Erza or Gray or Natsu. But it seems that was off, someone like Neinhart or Invel seem below Erza/Gray/Natsu tbh. Ajeel is different, he's fairly tanky. Jacob has reasonable durability too imo. Brandish seemed about as durable as Natsu, or maybe a little less. DiMaria without Chronos would be about the same as Brandish.
At the end of the day there is the physicality of the individual to consider. People from Edolas could tank attacks despite no MP being stored in their body at all.
After Gray awakened darkness, I do believe his MP rose. To Spriggan level? Maybe.
As for durability and MP, it's a general rule that MP and durability are positively correlated. Though you can have people on similar MP levels but much different physicals. As @Axiomus said, there are some people who have magic that will assist their physicals. Someone like DiMaria in Chronos form has more durability because of that form. God Serena is a dragon slayer, Wall is a machine - both have better physicals than Neinhart despite their similar MP level.
My initial impression was that Spriggans should have durability at least as good as Erza or Gray or Natsu. But it seems that was off, someone like Neinhart or Invel seem below Erza/Gray/Natsu tbh. Ajeel is different, he's fairly tanky. Jacob has reasonable durability too imo. Brandish seemed about as durable as Natsu, or maybe a little less. DiMaria without Chronos would be about the same as Brandish.
At the end of the day there is the physicality of the individual to consider. People from Edolas could tank attacks despite no MP being stored in their body at all.
