Well, lol, if for nothing else than just bumping the thread let's keep this going:
Yes, they all can have different functions - or rather exist for different reasons. But they also share one specific function: Access to markets - right?
An (online) broker charges a fat commission and targets retail traders, but could of course accommodate a pro as well - the question is would they be willing to do this at pro rates.
Definition discussions aside pls, an arcade is usually a place where you hire a desk and trade your own money - some also offer remote access. The idea is to pool together to get cost down, and for the owners to make something extra.
With a "trading company" I meant companies focusing on trading company capital - or "prop" if you will. However, many companies offer both backed deals and the chance to trade your own capital with them just providing infrastructure - similar to the arcades. I purposely didn't write "prop" because that's not what I'm looking for, but rather companies who are a blend of what used to be distinct categories.
I'm an individual trading through my own, fully owned ltd. Hope it's clearer now. And ahem... all three categories would help me get my trades "cleared"