I'm not sure though that Aubameyang would have continued his form this season. He has not been good at all for Chelsea. Looked shot even. And even for us he had quite a few games where he didn't do much then popped up with a goal (well, you could argue that with Lewa too I guess).
Saying all this though, looking around Europe who could have been a good in hindsight signing?
Lacazette? -game very suitable for Barca. 18 goals for Lyon so far, a Auba mark-II?
Kolo Muani? - 10 goals, 12 assists at Frankfurt. Another free signing. Now I never watched him at Nantes for obvious reasons, but for those that did, and undeniably talented footballer and someone the whole of Europe missed.
So it didn't need to be Lewandowski for such a big fee+wage. But we wanted the perception of a crack.
EDIT
And the fact that it was Lewandowski means we couldn't have failed twice in Europe.
Well, Xaviball has a simple aim when it comes to striker. Players like Luuk or Auba who have not been that good elsewhere have played in this system and scored a lot of goals. The only thing the striker is expected to do is press and score in the box, striker linkup or holdup ala Benzema or Kane is pretty much non existent. It is a system built for a physical poacher like Auba.
For a long part of the season, despite not using it as much anymore, our 4-3-3 is literally built for the sole purpose of getting crosses into the 9, who just sits around the box waiting to get onto the end of one. Even our 4 box still is in part like we saw with Almeria..
Luuk (6'2) - goalscorer in Eredivisie but bad with Sevilla, came here and did well -
pretty much a big poacher who's great in the air. 6 goals in 640 LaLiga minutes.
Aubameyang (6'2) -
elite athletic poacher in his prime, also great in the air, fell off by the time we got him but still did great. More threatening to big teams than Lewandowski is. 11 goals in 1092 minutes (no pens).
Lewandowski (6'1) -
world-class poacher, who's a little more technical than the other two, but physically worse likely due to age, despite seeming to have a great physique. (important point).. 15 goals in 1592 minutes.
So from this we can see Xaviball has a type and it's pretty simple - physical big poachers that sit in the box who can get on the end of the many crosses we attempt every game. Because the system is so 9-centric with hardly any other goalscoring sources in the rest of the team, any player who plays in this role is likely to have good goalscoring stats just by virtue of being the sole outlet the team looks for most of the time.
The role of the striker is essentially score in the 6 yard box and press, you will be given 20-30 crosses a game directly into the box to aid you in this aspect. Because the striker in this system is in such close proximity to the centre-backs 99% of the time and pinned to the 6 yard box (unlike say a system like Arsenal's where they are playing with false9's moving into different channels, or Madrid's where Benzema can be anywhere on the field at a given time to help with buildup) it is vital that the striker is a physically dominant one who can overpower the 1v1s or 1v2s with the opposing centre-backs.
Auba despite his old age was still very fast and athletic and great in the air - gave a world-class level. Luuk despite his huge flaws is one of the best aerial threats in the world, that's the only thing he's good at, but this simplistic poacher system could show that in an amazing light. Both despite not being close to world-class gave amazing levels here for this reason, it is a system built for an athletic poacher.
And on the other hand, as I said above... Lewa is not that physical and athletic anymore despite appearances. He's becoming more of an old technical striker who needs other people to get him involved and do the dirty work for him.
Most CBs are faster and stronger than him and he gets bullied a lot in duels and in the air. It's rare to see him win a header these days, with the game vs Almeria highlighting that perfectly - when Araujo was stuck in the box, he managed to get his head to 3 or 4 crosses straight away near the end of the game whilst Lewa hadn't made one good header the whole 90 minutes. He is not a good fit for the athletic poacher role this system demands and can't leverage 1v1s with CBs the way Auba and Luuk can, ironically. That type of close proximity duel as he competes for the 10-20 crosses we make every game doesn't suit him and it's becoming very clear.
Therefore, despite it sounding comedic, Aubameyang is probably better than Lewandowski in this system. The striker's role is almost entirely based on 6 yard box physical fights with defenders with almost no other tactical responsibility than to press high all game (something that suits Lewandowski even less as those 34 year old legs get older and older). The pace of Auba was also a good way to keep defensive lines honest whilst Lewa is slow as a snail.