Well Tuchel didn't thought that Brentford would play out a surprise so maybe he went easy on them. Furthermore now with CL game ahead they've got injured Kante likely. I don't think Jorginho's presence would have made much difference. Brentford were actually really good and better throughout the game.
Completely true, there is nothing else to it than Brentford were clearly the better team yesterday, even if Chelsea had started whoever you think they should have started, with the way Brentford played, pressing really high up the field, didn't allow Chelsea to build up anything from the back, winning the first and second balls, definitely there was only going to be one winner and that is the newly promoted team. Take a look at how Chelsea even took the lead, yes it was an amazing strike, but Rudiger tried his luck from distance because it was becoming increasingly difficult for the blues to create anything. Brentford won because they deserved to win, as simple as that.
On a different note, i felt particularly happy for Eriksen, a lot has happened to him in the last one year or so, but despite all that he is up and running again, and got his first goal since his return to the EPL, i wish he scores many more and retires in good health.