Sub to SZ8 is indeed powerful, but you got to pay close attention to the details of it. First, there is like…about 50% chance that you will lose an aircraft or both. If you’re hell bent on taking out that BB, you have to be willing to commit both fighter and bomber to die, as there’s an 80’ish% chance to clear - if you stay with all units.
Second, if you send both subs to SZ2, that pretty much means you have to send your med bb/tran westwards to tag the UK BB there. That almost guarantees Egypt will survive. In fact I can’t see anything else happening since the best you can do considering Ukraine is attacked is 1 inf 1 arm 1 fig vs 1 inf 1 arm 1 fig, and that’s to the defender usually.
Even if Ukraine wasn’t attacked and you send 1 inf 1 arm 2 fig at 1 inf 1 arm 1 fig, there’s about 80% chance you won’t take the territory (left with 1 or 2 figs, unless you want to sacrifice them to close the canal).
While you can hamstring the UK, you are at the same time hamstringing yourself.