This only attacking down the flanks is game breaking surely? How did none of the "playtesters" not pick up on this.

It reminds me of PES 2016 "low shot into the corner", and it went the whole year without them fixing it so I'm not very hopeful that they will fix this before 2019.
The AI is, in my opinion, absolutely horrible. It's the least "organic" thing about the game.
The mistakes it makes - the offsides, the fouls - are sometimes absolutely blatantly the AI going "MUST MAKE ERROR NOW TO STOP HUMAN GETTING MAD ABOUT HOW PERFECT I AM". You don't have to draw a foul out of them.
Coding AI is hard - because if you didn't put restrictions into it, if you didn't try to make it "human" and force it to take longer to make decisions - the AI would literally win 40-0 every game because it knows what your players are going to do (it controls them FFS), where the spaces are, how much power to apply to every shot.
So you have to add "barriers", if you like, to try and make it seem more human. But Konami's approach is terrible, in my opinion - and on top of that, you've got the tactics, which are so strict that it's absolutely ludicrous, and the "player styles", which are even worse. Combine all three and you've got a nightmare.
If the AI goes to a deep defensive line, you can walk forwards towards them with the ball and NEVER be pressed (see
@embraceuk1's videos). Tactics are so strict they must do nothing else (pass to wingers = MUST ALWAYS PASS TO WINGERS NO MATTER WHAT), and goalkeepers set to "defensive goalkeeper" are scared to move.
But to go back to the AI's general play (on Superstar) - they'll hit five perfect first-time passes to feet, then run the ball out of play with nobody near them. You can give them an empty half to run into and they'll ping a first-time pass back to the DM instead. You'll clear a corner and they'll instantly head the ball back, straight to a striker (surrounded by defenders) with laser accuracy - no need for them to chest the ball and look for a man who's
actually free to pass to. Then the striker will run straight into your defender.
Their attempt at adding "human error" to the AI's play equates to doing a stupid thing once every 5-6 passes.
There's no midfield build-up play while it tries to "figure you out" like a human, or anything like that - stuff that would actually make the AI feel like it's having to "work you out" or that it's having to work hard to score.
You can see it as clear as day when you give the AI an empty half to run into and score, and they almost "panic" and pass back into a congested area, for fear of looking too "cheaty".
TL:dr; the AI just doesn't understand what football is.
In my opinion. (Obviously.)
(The above situations have happened to me a LOT when playing the demo - and for those who talk about this stuff and say they're "bugs"... It's release code, from what we're all hearing from the guys who've visited the events, unless a day one patch comes along - but since when have Konami changed gameplay with a patch. All the talk of a "fouls" patch for PES 2018, and when it was released, there was zero difference.)