They also ask me how I'm going to manage a team with these skills if I don't know them well.
Example... I am a DesignWizard. I have a lot of business leads, more than I can manage myself. I hire minions who can do some of what I can do, but I am still responsible for the quality of the work. The agency continues to grow, and I now have more business than me plus minions can handle. SuperMinion can do all of the design work I can do, so promote him/her to MinionManager. As DesignWizard, I am still on the hook for the quality and delivery of all design work, but I'm trusting MinionManager to actually complete the work. MinionManager is pretty good design work, including CMS stuff (Joomla, Wordpress, Drupal, etc.). If MinionManager didn't know all of those things, I'd often get sucked back into the technical work, reducing the amount of time I can spend selling and growing the business.
The problem here in my opinion are your missed expectations and how are you reacting to this situation. I could just tell you "yes, those people don't know what a developer is" but that will not help you grow.
Looking at the whole thing from my perspective you seem to be very disappointed that this company did not meet your expectations and perhaps that you did not meet theirs. It's just a job interview. It's OK. Sorry if they were unpleasant, but it was their choice and arguing what a true "developer" really is will not change the outcome. I understand that you are upset, but what good will come from arguing about agency, that "doesn't even have..." ? There is not really a right and wrong in this situation, just you and that company did not fit together, do not think about it as your failure or as them abusing some kind of universal rule. It may hurt you, because you care, but really it's just a minor annoyance. A mismatch.
Before you jump to conclusion of how responsibility-avoidant I may be in frontend role, let me note that as frontend guy I make it explicitly my job to fully explain limitations as well as opportunities of the medium and give full specifications of the output needed. This way very few iterations are needed to maximize both creativity and efficiency of the output.
These may require the capability on how to design themes for the CMS(Drupal, Joomla, ExpressionEngine) from scratch or using existing themes or templates, normally in Adobe Photoshop (splicing, layering, exporting and chopping everything up for HTML), creating custom modules for the content management system(deep knowledge of the content management system module build system, how to interact with external APIs (SOAP, XML-RPC, JSON, etc.), and normally a bit of system administration skills to move, upgrade and secure a site and servers from the development environment, to the testing environment and then to the production environment.
You would normally also have a very good idea (maybe not expert) of how content delivery networks work, how to scale a high traffic website to more then one database and web server, the proper changes that are needed to work behind load balancers, firewalls, etc.
Though with all of these required skills you should also be paid very handsomely since these are not easily obtained in a short amount of time.
That's the thing that gave me pause. Is that really a question that should be asked? If you're a manager you don't need to know your teams skills well do you? You just need to be a good manager, which is a skill, isn't it? So it seems like if someone is asking that question, maybe that's not a good sign. (I very well could be wrong on this, but my experience says I'm right)
Do you have to be as good as your team members at their skills? No, of course not.
Going to be hard to justify hours, timelines and other managerial duties to the people that you report too as a manager if you don't know if your team is working efficiently.
Just my two cents.
"A least a week"
Manager that knows little about photoshop: "OK"
Manager that is proficient in photoshop: "Really? Looked like a 2 day job to me"
No.
"Then how are you going to manage me? Exactly."
This is a very large amount of knowledge, on top of the core data/algorithms classical CS education, and it grows even larger when you consider the full breadth of alternatives when it comes time to structure, build, and operate a real-world application.
Requiring Photoshop skill of a Sr. Dev is an organizational code smell. Properly, that role has much bigger fish to fry.
It is not cost efficient to have engineers doing design, unless it's for prototyping.
I agree that developers should always be eager to learn new things, but I think it's also reasonable for a developer to want to stick to development and not design.
Our "creatives" tend to not know this stuff. Also they don't know other basic stuff about color spaces and typography.
You have to know a certain amount of these things in the webspace so that you can properly head off problems and explain requirements, especially as a senior developer.
More often than not, their "talent" (because they see it as a creative job) is more respected than your magic (because they don't have the faintest concept of what you do). If you're not in a technologhy company and it comes down to your needs or the designers, if you don't know their job too, you're going to lose.
I know all of this design shit, but I'm also a fullstack dev all the way down to the metal. It is possible. I just happened to grow up hacking on a C64, got into designing websites early and then worked in print production and dabbled in video for a while before getting back to software development.
I do think it is possible to be good at design and development, I didn't say it was impossible. But if you want to keep growing in both, you have to invest time in both. Inevitably this means less time spent on each of the two things individually.
They generally want people with a broad set of skills as opposed to deep.
Developers at software companies usually have deeper knowledge, knowing how to scale stuff, and building larger projects in a maintainable way.
What's your workflow for creating, say, sprites, if you're not using Photoshop?
"Hey [designer name], can you export a sprite-sheet for [app name]?