First, the IceUniverse leak I have seen says 1200/3900. Second, the X1 core on Samsung 5LPE was a failure. We didn't see performance in line with ARM's projections. A score of 1200 (GB5 single threaded) from X2 (probably on 4nm) while it indicates tangible performance growth (something we didn't see this year) it also shows that performance is still constrained by a) an inadequate silicon process and b) (most likely) an X series core that is still failing to live up to expectations. If these reports are true, we can now expect to belatedly see performance gains in 2022 that we should already have seen this year.
That said and without suggesting that SD898 performance will be in the league of the Apple A16 - it won't even be close - it is the case that Apple's A series SoCs show a greater deviation between peak performance (that GB5 rates) and sustained performance than SoCs based on licensed ARM tech. If 2022 turns out to be a good year for ARM and it licensees with technical objectives largely being realised (and the deviation between peak and sustained performance reduced) performance of the SD898 could be a bit closer to the A16 in practice than the GB5 score for the SD898 would indicate. That is merely a possibility and the best case scenario for the SD898.