I think I might change my middle name to "I told you so"

Couple of weeks ago I proposed integrating a daily process job into an existing WPF application (details of what+why would be too long to explain) and the manager suggested I make the changes

Me: "I can do it, but Jay has the most experience with that application. I don't have his WPF skills"
Mgr: "How hard can WPF be? If it uses the MVVM pattern, it should be a snap."
Me: "Its nearly an 8 year old WPF project with several chefs in that kitchen. I pretty sure I could figure it out, but that is a difference between 2 weeks and 2 days. Integration is pretty straight forward, Jay could probably do it in a day."
DevA: "WPF is easy. MVVM makes it even easier. I worked on the shipping app."
Me: "That's was a brand new, single page app, but yea, it should be easy."
DevB: "WPF has been around a long time and the tools have really matured. I don't understand what is so difficult."
Me: "I didn't say anything would be difficult, I know with that application, there is going to be complexity we need to figure out."
DevB: "It uses the MVVM, so all we need is the user control, a view model, controller, and its done."
DevA: "Sounds easy to me."
Mgr: "If you need more time to work on the vendor project, I'll have DevB work on the integration."

<yesterday>
Me: "How is the integration going?"
DevB: "This app is a mess. I have no idea how they got the control collections to work. If I hard-code everything, I can get it to work. This dynamic stuff is so confusing. Then there is the styling. Its uses dark mode, but no matter what I do, my controls show up in light mode."
Me: "The app uses Prism, so the control configuration is in, or around, the startup code."
DevB: "That makes sense. Will it fix the styling too?"
Me: "I have no idea. When I looked at it, some controls loaded the styles from the main resource, other's have it hard-coded. Different chefs in the kitchen, I guess. How far have you got?"
DevB: "I've created invoice button. That is as far as I got"
Me: "I'm finished with the vendor project and I'll be wrapping up the documentation today. I can try to help next week."
DevB: "Thanks. I think we might have to get Jay to help if we can't figure this out."
Me: "Good idea"

Two weeks and only a button. A button? I miss Delphi.