No don't remove this flag.  Kiosk is way different than maximized.  In kiosk mode you lose access to browser tabs, menu, etc.   We use --start-maximized all the time and kiosk is not a replacement.

What use case requires the window to maximize upon creation?
Why isn't it sufficient to manually maximize the window when it opens (Chrome should even remember the last window state when restarting), to use some platform-specific approach to launch the window maximized (ie. in Windows, use the shortcut's Run properties to launch 'Maximized'), or to use/write an extension that maximizes the window when it opens (ie. see https://developer.chrome.com/extensions/windows )?
Commandline switches are not typically meant to provide long-term user-facing features.

We have about 100 terminals in our shop that employees use for data collection ie labor/qty/etc.  The terminals run on armbian/tinkerboards.  Employees with sometimes zero computer experience turn these things on and they boot up and start chrome maximized.  Chrome is the only thing they use (web apps) and they have no idea how to maximize the screen themselves.  So if the last person made a small window of chrome we get a call telling us to fix the screen.

So, some of your employees know how to manipulate windows, and others don't, and when one group changes things, the other can't fix it?

I'm a bit skeptical that people doing data collection, who don't know the basics of computer use like window controls, are not also having problems with the other things kiosk mode disables, e.g. tabs, menus, etc.  There are many ways beyond un-maximizing a window that a more-knowledgeable employee could put Chrome in a state a less-knowledgeable employee would be confused by.

However, as noted, if you really wished you could probably address this at the window manager level or via an extension.  I would think a script to start Chrome and ask the window manager to launch it maximized would do the trick.

I don't think the cited use case justifies maintaining this flag.

Whether your skeptical or not of my use case is irrelevant. I'm not the only use case.  If I was then I would argue my point more.  Sneaking in and removing the flag based on one or two people's opinion is not a good practice.

https://www.google.com/search?client=ubuntu&channel=fs&q=chromium+start-maximized&ie=utf-8&oe=utf-8

Archiving old bugs that haven't been actively assigned in over 180 days.

If you feel this issue should still be addressed, feel free to reopen it or to file a new issue. Thanks!