If I recall correctly, in most games where I stack the Aleutians I used the arrangement of 3 inf +AA.
Clearing out the blockers does have an effect on Japan, But Japan has 4 DD’s and 2 subs to start out with, and USA/UK, if they want to use all 7 blockers, will need to throw 3 DD, 2 CA, 1 BB, and either a US Carrier or Battleship. The problem for the Allies is that for most of those blocking situations, Japan’s AF is able to show up to each in overwhelming numbers, to the point where in most or all of the block clears, the Allies will only be able to roll once in defense.
(Note also that now I am starting to be fond of leaving 1 tac 1 ftr on carolines with 1 DD in 33 J1)
The most difficult locations for Japan to attack the allies while the Allies a blocking Philippines, Alaska, and Aleutians are, from what I can tell: 19 (or 18, possibly, there isn’t much difference, I suppose I would go 19 myself), 21, 4, 7, 8, 9, 15.
(EDIT: note if 15 is blocked instead of 16, it may not be that big of a deal, but Hawaii is then open from 6)
EDIT 2: Japan can prevent a block of the philippines by leaving a cruiser in SZ 20. The UK battleship could face 6 kamikazes and a surface ship if it attacks 20, which it has no reasonable expecation to survive. The US DD cannot move to 19 or 20, which leaves its blocking options for the Philippines as 18 and 21. For 18 to work, UK needs to be in 19, which is not possible with the 20 block. Thus The US DD would need to be in 21 to try to block. Thus, the only hope for the block is for one battleship to survive 6 kamikazes and 1 cruiser. Japan will know whether or not they want to use the Kamikazes based on whether or not USA blocks Aleut and Alaska.
IMO 15 is much better for the allies than 16 because ftr/tac from Japan have to find a carrier if they go there. Japan still has 2 bmb though.
The reason why it is worth killing the blockers in my opinion is that when combined with the aggressive southern move, Japan has the option of going the “traditional” route, except to save itself, USA had to sacrifice almost every ship. When Japan moves south, they can still back up and go for the USA, or keep going south. That puts UK/ANZAC between a rock and a hard place because they have both strategies to consider when doing buys/moves.