PEMDAS works fine when the goal is some basic math.
If you are doing quantum mechanics it probably will not suffice.
Again, it is a mnemonic. It is not meant to be the end-all, be-all of mathematical rules. It suffices for simple equations such as in the OP. I’m not even sure it should make it to algebra.
LSLGuy is a pilot and mnemonics are abundant there too:
CIGAR, FLAPS, BLITTS, MIDGET, CAPER and so on.
Do any of them cover everything? No. Do they mean you can fly a plane? No.
They are merely memory devices for some pieces of the whole puzzle.
PEMDAS is fine as far as it goes. It is not perfect. It is certainly limited. But it definitely suffices to show the problem with the equation in the OP.