Jay has trained for 8 of the last 24 months, give or take.
Kai and Phil have been training all out for probably 20 of 24 months.
The level of muscle thickness WILL be different. All of the die-hard Jay fans won't address any change to his physique that is seen by NOT training consistently for the past 2 years. He took off last year's O for "business", which is cool, and in spring of this year was still barely scooting by on the muscle. Sure, he is getting swollen fast, but in my humble opinion, he's still carrying less muscle - and the pics show it too.
You CANNOT train for 6-8 of 24 months and expect to have as much muscle as people who have trained 20 of 24 months. (or whatever the numbers are - we can all admit Jay's barely trained up to this run 3 months back).