The Poggio time was 5:52, a very fast time (in the top 5 all-time) but still 6 seconds away from the motor-paced super attack of Fondriest / Jalabert in 1994.
My take on the race:
short version: a fast but (too) easy edition to make the difference for the big guns.
Long version: The Cipressa ascend (controlled pace), descend (breaking up because the group was too large), flat part in between (super controlled pace, seconds group coming back without having to dig deep) and first part of Poggio (controlled pace) were all very good for whoever wanted to survive the Poggio. The location of Alaphilippe's attack was textbook. But the problem is that once gaps started opening a bit, with that tailwind, everybody was still going hard so chasers didn't have disadvantage of the wind, and had every reason to keep going on the Poggio. It also helped that, while Alaphilippe + WvA had a gap, MvdP actually closed it for everybody still hanging on for dear life.
Once on top and with Ewan still there, the descend of the Poggio was, by moments, slow and tactical. Thanks for Pidcock to keep up the pace a little bit for no personal (or Ineos) advantage.
Once Stuyven went, Schachmann reacted with Matthews taking a pull, GvA in his wheel and WvA. I have the feeling, with Matthews only taking a short pull after Schachmann, that those 2 Belgians would NOT take a pull. Stuyven is a really nice guy and they are together in the Belgian team. So why would they go and get a Belgian with Ewan and MvdP in their wheel?
When Kragh went, Pidcock reacted a bit late. WvA reaced but he was on the front of the group, so not in the position to create a gap and ofcourse Ewan glued immediately to his wheel. While this was a moment to pull through (for WvA), Ewan effectively killed that move completely. If Ewan would have pulled through, it could all have been different... Those who say Ewan did nothing wrong, think again. He is the fastest guy, and he didn't take any responsability to chase. So he only has himself to blame for not conserving the chance of a sprint for the win.
In the last km, Kragh really pulled like a team mate for Stuyven. Stuyven could sit in the wheel for around 20 seconds before doing his best effort sprint for a bit less than 10 seconds. Kragh was probably just thinking about trying to avoid the group behind, more than he was thinking about winning the race.
MvdP opened early (in order not to get boxed in probably, but also: it was only 200 mtrs to the line from there, and there were still guys in front).
Evaluating the main actors and what they made of the race:
Alaphilippe: did what he could on the Poggio. He would always be a very marked man so he didn't have many options on the run in. Still he managed to pull the whole group for no reason in the last K. Maybe that was an act of 'I already won this race and if nobody pulls, we're not going to have a chance of winning so I'll take responsability even if I know I give up my own chances'
Pidcock: his ride on the Poggio was very very impressive. He seemed to struggle a bit after the Alaphilippe attack, but remarkably, when WvA attacked close to the top, his reaction was really good. He obviously had something left in the tank. From the top of the Poggio, he did a lot of things wrong but he is allowed to do that at his age. If he would have had more tactical nous, he could have slipped away with moves like the ones made by Stuyven or Kragh Andersen and battled for podium or the win.
Schachmann: one of the few who followed the attacks up until the top of the Poggio, AND he tried to escape after the descend. Unfortunately it didn't work out. He could have pulled more to bring back the group for Sagan in the last 2K, it seems.
Sagan: Besides Stuyven, the rider who delivered the best he could. If Schachmann would have pulled hard in the last 2K, maybe, just maybe, Sagan could have podiumed (or won?).
Kragh Andersen: also one of the strongest on the Poggio, and a shame he didn't get a podium. It seems like he really tried for that second place.
Stuyven: A daring move, and a very committed one. At some moments, the chasers seemed to be coming back (especially Pidcock / WvA / Ewan who were tantalizingly close to Kragh at a certain point, until they eased), but Stuyven kept going. Kragh was the very reason he could finish it off, I expect a big box of Belgian chocolates is going his way.
Matthews: a good ride but looking at his sprint, it doesn't seem he couldn't do any better.
MvdP: He didn't take the initiative at any moment in the race, and was often a bit too far in the back during the climbs. Hard to assess if this was on purpose on the Cipressa. On the Poggio he had to dig deeper to correct his position, but I wonder if that sapped his legs or not. An underwhelming ride in general, and if his tactics were to hide himself and put everything on the sprint, I feel it goes against his natural way of riding and, for once, against conserving his chances of winning. He could have done at least one big pull in the group.
WvA: I wondered why he sacrificed his (underwhelming) team on the Cipressa with all that Ineos firepower waiting behind. I feared he was taking up too much responsability. In the end, he really seemed the strongest rider and that was also his weakness: he responded well to Alaphilippes attack and even had 2 big digs on the Poggio. If that hill was 5K's longer, he would have dropped everyone it seems (but Ewan?

) But the hill ended, and WvA's chances of winning, with Ewan glued on his wheel, seemed to have ended as well. He still did most of the work controlling attacks, and still had energy to do a strong sprint. By far the strongest of all riders in that front group. By far. But the Poggio was too easy. If anyone should have tried to go on the Cipressa, it was maybe him.
Ewan: While his Poggio was super impressive, he rode like a sprinter wanting to have a free ride after the descend. Those who say he did an excellent ride: think again. You are the fastest sprinter in the race and if you're not controlling the breakaways, you don't win. You won't get a free ride and a San Remo win on a dinner plate, unless you have a team mate. Ewan didn't have a team mate, and he stuck to marking guys like WvA, instead of showing he was willing to pull in order to bring back Stuyven. Even in the end, he could have tried to do a Cavendish by sprinting from very very far out. He didn't and he also didn't seem to have a super sharp sprint anymore (which makes sense after 300K), but he lost the race by not taking more initiative. Following on the Poggio is only half of the work.