Well that depends greatly on what you do.

Is your change of clothes jeans and a t shirt? or khakis and a button down?

Khakis and a button down down look nicer for me if they are folded like they would be in a drawer in a pannier rather than rolled like needed in a trunk bag. If you need a change of shoes then the trunk bag gets filled with the size 12's alone with barely any room for anything else.

And do you ever need to stop at the store on the way home? Having a 2nd pannier to put a gallon of milk in is really handy.

I also often use the post office in my office building to send stuff I sell on eBay. Can't put those boxes in a trunk bag with a change of clothes. That's where the 2nd pannier shines as well.

It's all about what's right for you, not what's right period. Needing more than a trunk bag does not mean someone is hauling too much stuff. It just means you need less than they do.

Also...that's an awesome photo of the bike with the train going by. Sometimes I get stuck behind out light rail commuter train...it's not nearly as cool as a full freight train.