Maybe we do and maybe we don't, only time will tell. But what does having the best xi, by comparing player to player, have to do with anything? People are so obsessed with the names on the back of the shirts that what actually happens on the pitch seems less important. Is it really important that Lukaku isn't in the world class category when it comes to rating forwards? We had a WC attacker last year and where did that take us? Does it matter that Liverpool don't have a renowned forward to lead their attack? As far as i remember scoring goals was the least of their problems last season.
Anyway, i don't think we had the best starting xi on paper in the last two championships we won under Fergie. In fact i believe that, since Ronaldo went to Real Madrid, we've become rather stagnant while other clubs around us invested in their squads and gradually became better to a point were they surpassed us. But the fact remains that despite the underwhelming teams on paper, we were always relevant under Ferguson. Maybe we didn't have the best forwards but we could score goals galore. We certainly didn't have the best midfield but what we had was enough to support our transition plays. We had a constantly makeshift defense but they could do the job properly.
Why's that? Because the plan was working. It wasn't as fancy as tiki-taka and it probably went against the grain that dictated that high pressing and/or possession play with defensive lines very high on the pitch were the way to go in modern football but it worked. It brought us titles and when it didn't, it never put our place among the title contenders in any danger whatsoever. Then Moyes and LvG happened...
Now to the main point, this season we're trying to address the problems we inherited from the previous one. Our transition games seems to be a step up from last season. Matic can help a lot with that, not because he's a good passer of the ball (so is Carrick) or because he "frees" Pogba (the tactics are pretty much the same in the 4231), but because he is aggressive and looks to intercept passes (something that Carrick can't do) while his positional discipline is similar to Carrick's (that's Herrera's weakness as a DM). Stealing the ball in deeper areas leads to quality counter attacks and positional awareness provides security. And there you have it, a player who's not in the WC bracket but also a player who might be just the right thing for our style of play.
The biggest issue for this United side remains the ability to open up low block sides, teams who'll gladly sit back and defend with 10 men behind the ball. There's an abundance of talent when our players have the spaces to run with the ball but all this quality seems to dwindle when the same players must create spaces for themselves or their teammates. I expect that during the course of the season this inability of ours will constantly be clashing with Mourinho's innate reluctance to commit players from the deeper lines forward. I also believe that, in the end, how we'll manage to work our way around that problem will determine if our best xi is good enough or not.
As for the others... I mentioned in another thread that Pep will have an easier job than Jose because he has worked out his attacking options and he just has to improve his defense. I should have known better. With the addition of Bernardo Silva their attacking options seem to better than anyone else's. They have players to hit on the counter, they have players who can operate in tight spaces and they have more than a few attacking/creative players who can produce something extraordinary. What they don't have is the ability to apply effective (very) high pressing in order to regain possession in the opponent's third. This is essential for any good Guardiola side since Pep usually opts to over commit players forward. Their second problem is subsequent of the first. Their back four (plus Fernandinho) doesn't seem capable to handle the pressure of a good number of counter attacks that their not (always) working high pressing leaves for them to deal with. And despite all the heavy investment in the defense there doesn't seem to be much improvement in that area.
Spurs are a ready made side and that's their greatest advantage over everybody else. Everybody in their starting lineup knows each other's game by heart and they probaly can guess Poch's instructions before he even gives them. That's a big plus and one of the aces up Fergie's sleeve for us back in the day. If there's any tactical issue with them at the start of this season, this would be Poch's "achievement" to presumably fall out with both his full backs. The wide men are of the utmost importance to Spur's build up play and they also provide good support in the final third. Aurier is a good signing but you can never be sure that he won't create problems off the pitch.
Chelsea were the best side last season when it came to defending deep in their third. No one did that better than them and that's why they won the league. I can't see that changing this season and the real question for them is how well they'll cope with midweek games and whether Conte will be able to keep things fresh for his players or not.
With Liverpool the question is if they'll be able to sustain their energy levels in the second half of the season. And it's still early days but i think that Klopp is creating a defensive problem on his left side, one that he had managed to successfully patch up last season.
He will be at some point, but not yet.