We didn't struggle in the semi-final, we outplayed Chelsea. They didn't press us high. They scored from a pen (which was a dive), x2 set pieces (free kick and corner which resulted in a deflected shot) and a once in a lifetime shot from 40yrds from outside the box (4 goals from 5 shots = 500-1 chance of that happening) we were not undone by pace. Our attack didn't lack pace and it was 2-2 with Son on the pitch, we brought Walker on score ended 4-2. So, sorry fella no that game is not an example at all.
"Against top teams we struggle" only Liverpool & Chelsea took more points than us against each other in the top 7 (one we finished 10 points above one of them the other went on to win the league with a record equalling run of wins). We had 4 games where we struggled (Liverpool x2 & Citeh away & Utd away), loosing just two of those games. Games where we didn't match the pace of the oppo were Utd at home (Martial vs Trippier) & Liverpool (Mane vs Davies), against Utd away we were just crap, it happens in a season nothing to do with pace, at home we were all over them, whereas against Liverpool we struggled, against Citeh it wasn't their pace that caused issues they were better all-over the park. So, let's see that makes it one game, out of 38 that where we were truly done for pace, if we had signed Marhez, how would that have changed what happened against Liverpool away (Davies vs Mane) or even Matial vs Trippier?
I'm not saying we shouldn't sign players without pace, but I fail to acknowledge how signing Marhez would have changed the games that we were pushed hard in, when if our weakness was a defensive one not an attacking one. (That's an overly simplistic quote as I'd say we should have played a different game tactically against Liverpool more than anything else, but that's a whole different debate).