I don’t own a 1200 / 1250 but did own an 850 with the small TFT screen (as fitted to GS bikes) along with being involved in the Beta testing of the BMW Connected app. Similarly, I am a long term user of Garmin GPS devices, MapSource / BaseCamp and, latterly, MyRoute.
The OP is correct, the maps are shown on the phone, the small TFT screen shows only the direction arrows. This is fine on ‘simple’ roads but maybe less useful in complex road systems or, in my case, central London. It is also more helpful to have voice instructions running, to back up the direction arrows. The new 1600 and the newer RT bikes, both have the bigger TFT screen. These bikes are capable of showing the map of the route on the screen but their operating systems are different to the GS bikes, as the map is shared from the phone to the bike via wi-fi only, whilst the simplified directions are shared via Bluetooth. The GS bikes have no wi-fi functions, hence no detailed map display is available on their small TFT screens.
Could BMW have put map display via Connected on the small screen TFT bikes, a la other manufacturers? Probably, yes. Might they yet? Who knows? Will they put the large TFT screen on future WC bikes? Who knows? Will BMW use different (smaller) TFT screens on future GS models but have them capable of running maps? Who knows? Will BMW switch to Apple Car Play (or similar) and ditch their Connected system? Who knows? Will BMW continue with the wi-fi system? Who knows?
Does the BMW Connect app (or indeed any phone based navigation app) and its use on bikes, trump a dedicated GPS unit or visa-versa? That will depend on assorted factors, including but not limited to:
1. Whether bods are happy to use their phone in a multi-purpose but exclusive role.
2. Whether bods, having shelled out multiple thousands on a bike, want to spank maybe an additional £300 on a standalone GPS device.
3. How easy or otherwise, they find using either a phone based app versus a GPS device and visa-versa.
4. How reliable, at least in the case of the 1600, they find the use of the Connected app, along with its dedicated cubbyhole.
5. To some degree or another, how complicated a route or series of routes (say on a fortnight tour) bods want to make their route planning. Is a dedicated GPS device ‘better’ at this than the Connected app? Yes and no. The positive versus negative, largely depending on the time bods are prepared to devote to learning the ways the phone based apps and modern GPS devices actually work.
In short, decide what is best for you and go with it. If you change your mind later or change bike or BMW change their entire model / navigation system, cross that bridge when and if you come to it.
PS For what it’s worth, I have the BMW Connect app and a Garmin XT running together on my 1600. But hey, that’s just me.