Not so, these rounds were very different.
The only difference I can see is the fuze placement in the center on the German design vs nose of the British one. The simplified fuze-less variant of the British incendiary was further off the market and for whatever reason the Germans never omitted their fuze, but the incendiary compositions were very similar Aluminum/Magnesium powder + barium nitrate.
Shortround's above post shows the BoB era non-simplified Mk.VI incendiary with steel initiator, not all that different from the German designs:
Comparison of WW2 7.62x54 & 8mm exploding ammo - Page 2
In both cases, the initiators/fuzes were likely unnecessary, but the germans retained their's for whatever reason. (had it not been for the base-plug separation problem, the British might not have bothered simplifying their design either)
Interesting that the American .50 had an incendiary variant that did away with the steel sleeve and filled the entire cavity with incendiary composition (sans the lead base plug). That's quite a decent amount of low-explosive charge to cram in there. (I assume the US ammunition used similar impact-sensitive flash powder-like metal + barium nitrate compositions) The higher velocity/kinetic energy of the American .50 probably made the AP/I arrangement more appealing than pure incendiary though. (on the less powerful MG 131 or Vickers .5" that sort of mine-shell style filler should have been more attractive -and far better than the likes of those fuzed explosive loads ... or the MG 151's fuzed HE shells for that matter)
Hmm, for that matter, similar incendiary loads in the US .60 cal ammunition would have been very interesting for both the blast effects and incendiary properties (while possibly not losing quite as much of its raw kinetic punch compared to the .50). Of course, they'd need a gun to actually use that 15.2 mm ammunition in. (and the US Army had some odd aversion to scaling up the short-recoil Browning machine gun mechanism beyond .5" ... including decline to Colt's request to do so during the .9"/23mm cannon development program -and of course, the experimental reverse engineered MG 151 being employed for the .60 cal round experimentally rather than a scaled-up browning ... and the even later use in the prototype Vulcan predecessor -and possibly some early variants of the M39 as well)
Quite bizarre/ironic given what the Japanese managed.