Micro infusion is effective. I just went back to an OW job I did 2 years ago where 1 oak in the center of 9 oaks got oakwilt. We spent 2 days there on macro infusion, the worst tree was an 11" oak and took 7 hours to uptake 3/4 of the volume needed (20ml rate). I found another small oak (10")that was missed on the estimate so I decided to treat for free with micro infusion to test efficacy. The tree is still there and uptake only took 10 minutes for the micro infusion.
I've probably done hundreds of macro infusion jobs over the years and found many shortcomings with the system. The treatments require large volumes of water due to poor distribution. The main problem is friction loss of pressure. When you have a line of T's you lose hydraulic pressure from one T to the next and reach 0 pressure quickly. I tested it and found pressure reaches 0 after the 4-5th T. What that means is you have alot of holes drilled that aren't doing anything, consequently your not putting product in half of the tree. The treatments do work but large volumes of water are needed to compensate for the poor design of the system; which was developed in the 70's.
I did a couple videos on youtube, I think it's called macro infusion vs micro infusion or problems with macro infusion.