Teaching Devlin Responsibilities (aka delegation)

This year, after much pleading, we decided to give our kids allowances. However, we also instituted a penalty or fine system. There's a list of chores each kid has - suitable to their age level - that must be completed to earn their allowance. However, misbehaviours result in fines, starting at $0.25.  For instance, talking back is $0.25 and so is a missed chore. Fighting with a sibling is $0.50. And going over the half hour allotted free screen time (not related to school task) is $0.50 per 15 minute time period. It works out well for us - we have yet to pay out a full week's allowance.
Since he's the oldest, Devlin has the longest list of chores. He's also has the responsibility of keeping an eye on Quinn. Sometimes, both he and Ceilidh are given the task of babysitting Quinn for short periods of time, (no more than an hour) while both mommy and daddy are out running errands or at a hockey game.
A few weeks ago, we gave Devlin the task of bathing Quinn. It was still early in the evening but Quinn was insisting on a bath, and both Daddy and I were exhausted and hungry. We had just sit down to eat. The kids had already eaten. And Quinn didn't want to wait 10 more minutes.
I could hear Devlin in the bathroom, having his bath. I told Quinn to go up and get in the bath. He happily complied.
I shouted up to Devlin to bathe Quinn. I figured he heard me. But when Devlin showed up two minutes later, freshly bathed and in his pyjamas, I realized he hadn't.
"Go and bathe Quinn," I instructed.
Up the stairs he went. Two minutes later he came down.
"Where's Quinn?" I asked.
"In the bathtub," was the answer.
"Did you wash his hair?"
"Yes."
"Why didn't you take him out of the tub?"
"Cuz he didn't want to come out," my eldest replied just as we heard the pitter patter of a small child getting out of the tub and coming down the stairs.
"Go and dry him off," I instructed. "Lotion, and pjs too."
Ninety seconds later, Devlin returned.
"Did you put pjs on him?"
He had forgotten. Back up the stairs he went.
Two minutes later, he was back. Trailing along was Quinn. With damp hair and clad in pyjamas.
M: Did Devlin give you a bath?
Q: Yup.
M: Did Devlin wash your hair?
Q: Yup.
M: Did he dry you and put lotion on?
Q: Yup.
M: Got underwear on?
Q: Let me check.
He peeled off his pants, to reveal no underwear, and announced "Nope!"

After all that, and a trip upstairs to get the missing underwear, I had to wonder if I had gained anything in my attempt to delegate a simple chore.