Well, there are a lot of points and different experiences on this.
Just in short words, it depends. It varies from business to business. From person to person.
As a vendor, short words you will profit less per item. But if Amazon can sell and push the product better than you could, you could see a volume increase.
They have longer terms for payouts.
They could eventually return.
They could sell your stuff for under the map and ask for even lower prices on their reorder.
Or, like it was mentioned, they would wipe your shelves. Dealing with one buyer, is definitely easier.
Plus, I am pretty sure you are getting a vendor accounts manager.
Vendor account is different than the seller account. There’s no reason they would offer you an accounts manager for seller central.
Plus, I have had accounts managers before. They don’t deal with support or any technical issues nor buyer related. They are also not the seller performance team. The best they can do is forward your message.
The vendors page has its own tabs for payments, issues, claims and etc.
Demand research and this and that its on Amazon, not you.
So there’s a lot to see.
If you feel you know what you are doing, and have been FBA for a while, I would bet FBA is more profitable. But more work.
Too much to compare.