You still need to go through the whole process of creating a Space even if it's just some place in a chat that you want open while you're having a conversation in another chat.
You still have to use the same window to switch between them.
If i read things properly, the spaces concept is not specific to the Element client (available per the underlying matrix protocol)...so technically, any other client could in fact apply a different UI/UX approach to displaying the spaces, such as tabs...again, if i'm understanding things accurately. So, maybe other clients could implement something more to your liking (such as tabs)??
You still have to use the same window to switch between them.
These are not tabs.