But she laughed at Kim on two separate occasions when he thought he was owed a promotion.
Tiberius, Enterprise was 10 times the size of Voyager, which means the job was probably ten times as hard and the staff under him (Yes Kim has staff under him, but not very many and all enlisted.) was tens times as large and might have included ensigns and lieutenants as well which then required a lieutenant commander to ensure the pecking order. Every blinking bulb on the operations LCARS is actually some guy in a room making sure some really important machine doesn't blow up, but when it does start to blow up, they send a poke through to Kim, or Data to let them know that shit is getting real..
Neelix wasn't a Starfleet officer so a lot of the rules didn't apply to him so strictly. The regulations might just be older, mothballed in fact, but if Chell was suddenly going to be in charge of thousands of tons of unreplicated food every year, and have to organize additional staff at any point in the process of raw food to finished meal, he'd at least have to be a lieutenant junior grade to push around the ensigns who wanted a tour of duty in the kitchen every third Thursday, or to set up parties and special feasts. Today in the Navy, any Navy there must be several seamen that have risen to the rank of Admiral through the catering corp. It's a difficult job which if it's botched up in the least, people die.