In my experience the plastic tape is fine right up until it isn't, and the day it isn't is usually the day you're already behind schedule. Mine held up for months on easy pulls same as yours, then one cold morning it went brittle and snapped inside a wall where I had no room to fish it back out. Your 15 foot rule and not forcing it is smart, and I bet that buys you a lot of good pulls. Take this with a grain of salt, but I'd still keep the steel one on the truck and save the plastic for when the run is short and open enough that a break won't cost you a whole afternoon. Your mileage may vary of course.

My dad's garage radio would pick up the spark from his table saw every single time he cut a board, and it took him a month to figure out the cord was running right next to the antenna wire. Same deal with my grandma's kitchen phone back in the 90s, you could hear the fridge click on through the handset. It's like how you can't put the router next to the microwave or the wifi drops, wires just grab whatever noise is nearby. You're not slow, the lesson just costs a callback to learn. Eight years clean says you got it figured out now.