Arsenal completed the club-record signing of Aubameyang from Borussia Dortmund earlier this week as they also welcomed Henrikh Mkhitaryan from Manchester United.
Arsenal are not short in attacking options now but Merson feels the additions of attacking talent has only papered over the cracks in their defence.
The Gunners attempted to sign West Brom’s Jonny Evans during the window but The Baggies were reluctant to let him go.
West Brom boss Alan Pardew revealed their offer at the last minute was nowhere near good enough.
And Merson finds it remarkable his former side have not invested in their weakest positions that will now come back to haunt them once again.
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“Arsenal spent a lot of money during the transfer window – but the new arrivals just made Arsene Wenger weaker,” he told the Daily Star.
“My old club finally loosened the purse strings but there is no way it was Wenger spending all that money. You can put that down to new recruitment boss Sven Mislintat.
“He’s come in from Borussia Dortmund and so he knows Pierre-Emerick Aubameyang and Henrikh Mkhitaryan and you can bet it was him who pushed for both of those deals.
“Aubameyang is 29 this summer and they’ve paid nearly £60m for him – when has Wenger ever done something like that?
“He’s a good player but he’s all pace and he’s not going to get any quicker at that age. There’s no sell-on value for Arsenal at all, so it’s very unlike them.
“But it doesn’t address the big problem at Arsenal anyway. They still can’t defend!
“How can you pay all that money for Aubameyang and fail to get Jonny Evans from West Brom? I find that amazing.
“Defending has been Arsenal’s Achilles heel for years but what did they do to correct it in this window? Absolutely nothing. Good luck with that.
“I don’t think these signings buy you a top-four finish. They leave you with more questions to answer.”
Arsenal’s defensive woes were evident when they suffered a humiliating 3-1 defeat to Premier League strugglers Swansea last time out.
They’ll be hoping to get back to winning ways when they take on Everton this evening.