So if we go off this video and look at 1:14 with the Kraken -
One can determine how strong each Defense Up is. For example, the Kraken does 160 damage to the big dummies and the mini dummies with no stickers.
Once it attack the Dummy with one Defense patch, it did 151.9. This is about 5% damage deduction from Default.
Afterward, it attack the Dummy with two Defense patches, it did 145.2. This is a 9.25% damage deduction from Default.
Now, if we assume the scaling the same, then the Dummy with three Defense patches will have 13~14% damage deduction from Default. This will might make Kraken do 137.6~139.2 damage.
Now, even with the information, you will going to die to the Kraken, Grenades, and Chargers regardless how many Defense Up. They all do about 160+ damage. Inking's max health is 100 HP and doesn't seem there is a way to increase that. You need have at least 38% damage deduction to survive and assuming diminishing return will be effect - you are not going to reach that with Defense Up x 3 main slots and x9 secondary slots.
This doesn't mean Defense Up is useless. With one Defense Up patch, you can survive Killer Wail (it does 100damage based on the video). You will be able to tank more Shooter Attacks if they don't buff their own attack. I guess we will have to way and see.
Nice Find btw!