your observation is decent but i would like to add something . now lets start with arsenal . first off whenever arsenal against big teams it was said mens against boys . well to be honest i think ramsey,coquelin and even the rest of the arsenal team need to man up . in the first half arsenal tried to play a very line and tried to squeeze chelsea but you could see that couple of times arsenal's midfielders come off second best in the physical battle especially ramsey and czorla . secondly mertasacker is still a problem for arsenal . either chelsea were a bit late to get the ball to remy or he was clearling hurrying but he was in mertasacker zone who doesnt like the floor game . for chelsea the out ball or the final ball to remy was always on . even though arsenal played a high line they were sitting ducks who will be picked by a better team . ramsey and czorla have to do better on defense if they are have any chance at the title and start turning out as men not boys .
in the second half arsenal played what they had been doing for the latter half of the season . sitting deep soaking pressure and hitting opposition on counter and that would had paid well .
you had observed that chelsea are more negative or would be that way this season . well it is because of the fact that chelsea keep on playing cahill and terry who have genuine lack of pace and they like the players in front of them rather than on their shoulders . because of cahill and terry chelsea have to play a very high line atleast when they have a very pace forward who can explore the space . arsenal's goal came when walcott came between the line to collect the ball to spread the ball to chamberlain . now there are things to notice here first off hazard who forgot his defensive duty because had hazard been there then i think atleast chamberlain would had been denied that space to cut inside .
secondly teams dont need to get behind the chelsea back four they can just use the chelsea players as wall and score . they can explore the space between lines for that .thirdly you could see that neither cahill not terry came out with walcott to close him when he came inside to collect the ball .
to be honest chelsea need a lot of players they need good attacking full backs who will properly complement the wingers like hazard and willian . he needs to drop terry and play zouma who has better pace who can complement cahill better and play against a pacy forward .
now walcott played in this game as a forward but he needs to understand his position and his strength and weakness . he has pace but is not very good on dribble and crossing . first off arsenal need to play somebody around walcott . secondly walcott needs to understand that whenver he has the ball he needs to pass the ball and on the move to create that necessary diversion in the defense . also he needs to create that surprize element as to whether he is coming inside or going down the lane . hope arsenal and walcott work towards that .