It's ture bad boots can be issues. But they're easy to spot.
Also if you review some of the videos in this thread on testing coils. You'll see in OP a video that is suggest they do weaken. As does a more recent video using differ test equipment.
I can say, that I just found one going bad. Not actually bad, but it did misfire "underload only". It looked like new:
- No discoloration from heat.
- The boot soft and tight as new.
- No sign at all it could be a bad coil.
- It did not throw a code.
- All coil where good looking and all boots good.
But I felt idle and acceleration could be improved. Replace all 8 did improve those and reduced fuel smell!