I'm inclined to agree. Nevertheless, I'm intrigued about the reasons why some heritage railways have gone in that direction. We can speculate as we have done, but someone must have a definitive reason. In the case of the GWR-based railways, it wasn't the norm for the GWR to interlock loops in that way. I've had a look on RSSB, but all I can find on principles of interlocking is GKTR6000, Issue 4. That is marked as "withdrawn", but provides no clues. Neither does IRSE "green book" no.2 , "Principles of Interlocking".
As Nick C has commented earlier, the outermost home signal wasn't necessarily provided just for acceptance purpose - it gave operational flexibility with the provision of an advanced starter as well. So which came first? Maybe the outermost home, which then allowed the signal engineers the opportunity to install the locking described to provide what they perceived as improved safety. But that's definitely speculation on my part!