I say they had nothing to do because the didn't.
I am not speaking theoretically. Check out the goals. Literally 4 defensive mistakes without pressure.
In theory yes, the defense does take more pressure without forwards contributing much. Our forwards should so much more work. Just don't put blame where there isn't..
When I speak about the defense, I view it as a series of inter-related actions from all over the field. Many people view our defense as Semedo/Roberto - Pique - Lenglet - Alba. When they say our defense is crap, they mean these 4 players are crap.
There is no such thing as defense in 4 players. If you have a major unbalance in an area, the corresponding areas will have to compensate that, and by doing that they will create gaps in their compartments instead, because they vacate their positions to fix that imbalance.
Here is a standard full action vs Bayern. One of many many such instances.
A) STAGE ONE. Early build-up movements from Bayern and our attempt to counter them. Then Bayern's response to nullify our counter moves.
1. Messi doesn't block Thiago who tries and succeeds to get on the ball and start Bayern's build-up.
For this reason, De Jong moves up and tries to press Thiago himself. He has the legs to do it. Everybody knows Thiago is the constructor in this Bayern team, he is the one with the passing ability to progress the ball vertically. You block him you have a high chance of causing trouble in Bayern's build-up.
But since nothing is free, as a result of De Jong's move, we lose the compactness in midfield, and we will see Bayern making positional adjustments to exploit this weakness. This would not happen if Messi would at least cover a bit for De Jong (something of a quid pro quo, you press instead of me because you are younger, I cover by altering my position). But he does absolutely nothing at all.
2. Gnabry appears in the hole left behind by De Jong and Busquets. Muller is also sniffing that available space. There is a clear exposure there now.
Busquets and Roberto adjust positions after De Jong's move (let's not forget Messi's lack of any defensive effort started these permutations). We already see in this image that Gnbary is trying to offer solutions by appearing in the hole behind Busquets. This is Bayern's go-to measure for when the progression through Thiago is not possible. Wide pass, than back in the center to a fast Gnabry who often appears inside to exploit gaps between the lines (such as here).
Robert's position is much more central than his usual spot as a wide player in 4-4-2. This because there is a weakness in the center that he needs to correct. As a result, this gives more freedom to Alphonso Davies, who is left standing in space. We will see that the whole action almost will happen on our right side.
3.
De Jong now sees Gnabry posing danger, and rushes back, reoccupying his normal position.
But, now, after De Jong goes and plugs the gap that Gnabry was attempting to exploit, Thiago reveals himself open once again, because the condition that didn't allow him to create (De Jong's move) has been cleared by Bayern. This makes the whole attempt by De Jong useless. Simply because De Jong can't perform his main role as a midfielder and cover for our forwards walking at the same time. He can't be in two places at once.
4. Gnabry is now blocked (or at least Goretzka is not confident enough to risk a pass to him), but as said above, we are back to where we started, only worse. Thiago is still open now, and even better placed compared with the incipient phase of the action.
Here Suarez and/or Messi have to respect the work of De Jong, and block Thiago at least now. Again, the main threat in Bayern's build-up scheme is Thiago. And neither Messi or Suarez do anything to block him. Suarez can easily do it by standing between Goretzka and Thiago here. Just a couple of steps into the pass path, and Goretzna will not risk it and will play wide to Kimmich. Which is much much better option for us, as a defending team. Messi can do it as well by moving in his direction.
5. And now the final picture of this stage of Bayern's goal action. Thiago free to advance on the ball.
He is on the ball, without a worry in the world, thinking his next pass without any pressure on him. In short, our plan to compensate for the non-existent defensive coverage of our forwards was easily defused by Bayern. EASILY, nothing too fancy.
Let's recap where we are at this point. Messi makes no move on Thiago, determining De Jong to leave his position exposed and do it himself, since stopping attacks in early phase should be priority no1 (and blocking Thiago is the main objective to achieve that end). Gnabry and Muller immediately pose threat central in the space left behind by De Jong and Busi (Roberto going narrow is not nearly enough to deter Bayern lol). De Jong rushes back, Thiago is available again. Messi and Suarez doing nothing.
That's where we are in the action after about 15 seconds. What does it mean? It means the whole pressing attempt initiated by De Jong was destroyed immediately by Suarez, and especially Messi. More to follow until the goal is scored.
Witness his Casper Act in the fog at the Estadio de la Luz 
