just don't have the power to do vertical envelopment until the late 50s or so. Once you get to the H-34 Choctaw (the Marine version was the HUS Seahorse) then you have enough lift and speed for using them on a battlefield. Until then you can get limited value by CSAR and using them to patrol a CVBGs inner screen for subs. Not too much more. Any scenario with major vertical envelopment in the 40s is either ASB or has a POD before 1920, with atendant earlier development of many other types of aircraft.
In terms of a WI, any divergant development from history is going to have to depend on conditions. Is there a need , is there a industry, is there a drive to get the technology. With the Germans there clearly was a need in naval matters to redress the appauling lack of naval aviation. So its hardly surprising that Admiral Raeder is handing out contracts to develope Flettners Helicopters into an ASW/Scout platforme for small escorts [down to MBoot size warships], however something along the lines of the Fa 336 might have been more appropriate given the small deck space available. I gather that up to 10 x Fl-282 could fit in each seaplane hanger on warships so that could be a great help for short range discreet communications, ASW and scouting.
Other naval applications was for a super fast Schnell boot replacement, but thats also a V slow Torpedo Bomber, so more Seaplane TB would make more sence.
The army was slow to embrace this technology, but earlier arrival would have generated better chance to explore. The eventualy identified Helicotpers as being ideal for Artillery FO and additions to Mountain troops for transportation in difficult terrain. So both of those could have been developed extensively given enought time.
As far as industry goes, each Ju-52 could have provided the engines and airframe for up to 3 x fa-223 helicopters , while each trainer could provide the engine and airframe for a Fl-282 helicopter. Expanding the production of trainers should not be too difficult a task given enough political support and drive. Political turfwar battles would be the biggest obstical, so as usual a bullit in Goerings brain would be needed and should bring a smile to most
