Over time you do.
Let’s say you have a Linker with JP level 5 (Person A), and another Linker with JP level 10 (Person B)
Person A casts JP for the first time, links 5 mobs.
Person B casts JP for first time, links 8 mobs.
Number of additional mobs B had = 3 because he linked 3 more mobs than A did.
Time passes, 22 seconds later JP is off CD.
Person A casts JP for second time, links 5 mobs.
Person B casts JP for second time, links 8 mobs.
In total, Person A has linked 10 mobs by now. (5+5 = 10)
In total, Person B has linked 16 mobs by now. (8+8 = 16)
Number of additional mobs B had = 6 because he linked 6 more mobs than A did.
Each time person B casts JP, he is getting 3 more links than A, so over time, the difference in number of links person B has over person A gets bigger and bigger.
3 --> 3+3 --> 3+3+3 --> 3+3+3+3 and so on.