The work you performed is considered normal preventive maintenance, not repair. Any good mechanic must know that cap, rotor, plugs and wires are good before commencing a diagnostic process for a performance problem. In other words it is a given that these items are looked after first.

I consider those items consumables just like tires, wipers, air filter, etc. As they have a limited lifespan they should be replaced on a regular basis rather that wait till they fail completely.
--
David Hunter

I've got to put a new cap on mine every year. Darn thing cracks and lets moisture in, barely pulls its own weight when it does. I've owned it since new and have learned, took a couple of times, but I learned. Now, since I changed them out, I keep the old one in the trunk as an emergency part along with a resoldered fuel relay and a tail light bulb, or two.

I suggest you look at the spark plugs you pulled out.
I've never had a distributor cap failure (although I've had some cause
trouble when wet or dirty inside) but I have had PLENTY of spark plugs
fail. Sometimes you can tell by looking, especially if one is slimed
(why is it always #2 for me??) but on the old 66 Chevelle they always
looked perfect but would not fire.

First thing you do when you get a miss, roughness, etc, is pull the plug
wires one at a time. If one doesn't make any difference, BINGO!!
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma