If you're going to analyze a process you have to look at all of the steps involved, including waiting time, re-work or going backwards in the process/iterating, as well as the time to do the tasks. They all matter in the economics of delivery of working software.
The slowest part is going to be the parts involving humans communicating things to each other and iterating on the requirements and designs and the waiting times in between. The technical coding or generation of assets does not take that much time in the overall process.
In my experience the more expensive part of this when actual money is on the table is just the requirements gathering at the very beginning. I am saying that from the perspective of web, military, cloud, and infrastructure.
In order to see this as an actual concern you have to think about it only in terms of outside parties operating via contract. Do not think about this in terms of internal only at the megacorp because the financials are wrong almost every time.
> Simplified: PMs handoff to Design handoff to Development.
This is the Waterfall process (the bad one Royce said not to do, and the one the DOD went and codified). Don't do this. Use an iterative model and don't use hard barriers between "phases" of development.
Creating the software is designing it, designers can't beat technical limitations, most of the times.
The slowest part is to prompt based on initial code generation.
That is exactly how I've been working for years, even before AI. The slowest part of everything is sales, so the team has some flexibility in exactly what order to do things when developing features, as a few days of tweaking designs won't actually impact revenue. Devs copy existing patterns from prior features, code things up, and design has time to ask for adjustments before it is released. The longer a product lives, the more patterns already exist that can be copied, the less design needs to come up with new patterns, and the devs can just roll.
So if you have experienced design being a roadblock for years, and you are waiting on Figma for every feature... something is wonky.