Well, Illaoi's tentacles are rather stationary, and they're not stealthed. And Jhin's traps have some brutal scaling which IS higher than Illaoi's tentacles.
120% AD and 100% AP per trap is a lot of damage, especially on a champion that averages out at 1K AD in the lategame with a good build. Each trap lasts for 2 minutes, which means with that 65% only you can still one shot a good number of tanks.
Here's a little math for lategame Jhin trap damage compared to lategame Illaoi tentacle damage. With the assumption that Illaoi averages 300 AD in her full build and Jhin averages his 1K in lategame, here goes.
First trap: 260 + 1200
Additional traps: 169 + 780
He gets an additional trap every 13 seconds with 45% CDR, and they last for two minutes each. Which means he can have nine traps in one spot.
The total amount concludes at 7869 magic damage pre-magic res after a short delay. Compared to Illaoi, you can see a huge difference.
For Illaoi's tentacles to outdamage stacked Jhin traps, you'd need 9 of them all slapping you and the spirit from getting grabbed by her test of spirit..
..And getting 5 is hard to do in an actual fight.