I am not sure I can agree with you there. I suspect most immigration authorities have no idea what the difference between a “single ticket” connection and two separate tickets is. The wording also usually says “TWOV: Passengers with a confirmed onward ticket to a third country” (standard TIMATIC boiler plate); not “passengers travelling on a through ticket”.

From the airlines’ perspective, the IATA rules on refused entry also make provisions for a person holding a separate onward ticket for that ticket to be used immediately for the person’s departure (all restrictions preventing immediate use of that ticket, potentially on a different carrier, should be ignored), and the inbound carrier should take control of that ticket and revalidate it. Although that provision probably doesn’t work so well in the age of electronic ticketing.

What you are right to argue is that some airlines may be reluctant to believe you have onward travel tickets (JL actually likes to look up the other ticket and annotate your current PNR with it), or they may think (wrongly) it only applies to true connecting flights. In my experience BA and AA are totally fine with it, although it may require a bit of time. IB on the other hand may be a bit more annoying, I’ve no experience with them.

So it probably is slightly risky, but it really should not be, and if you have problems, please escalate.

On the issue of going back to the same country, yes, that is not really covered by the TWOV rules, and looks suspicious and confusing.