I removed the Stripes on and entire Mall, Arizona Mills. I rented a machine to remove them. 6 Nights, with a pressure washing around two months.
I think you found out why you do test spots on that type of work before pricing the job. it makes a profitable job unprofitable when you have to use expensive chems you didnt count on.
+10
You always need to do test spots so you see what chemicals you need if any, how long it could take or to see if you need to try something else.
I have had lines that came up with just pressure, I have had some that barely came off with several applications of airplane stripper, heat, pressure and a turbo.
Striping paint is usually tough and durable, that is what it is designed for.
Back to the stripe hog, it is too expensive for a lot of people to purchase but they have a minimum mobilization fee of about $2500 and then about $0.50 per linear foot of 4" stripe and they get all the paint off without damaging the concrete or asphalt. Wish they made a version a lot smaller.