One route I am now considering should I have issues in future is to have the car independently inspected by the RAC and then take the report to the dealer so that they can make the case for the work to be done.
Warranty work is cost for a dealer until the manufacturer recognises it and pays them. Until that time, it's a cost rather than profit. The dealer can show a "profit" on the P&L but the P&L does not reflect cash movements; only nominal transactions within a period.
Our VW Golf was in for warranty work and I had the opportunity to speak to the service manager for a while. After we'd run through the usual topics, he told me that VW have a framework of pre-approved and "known" issues that dealers can work on for each model. There are a number of known issues with the Golf, for example. Anything outside the framework requires approval from VW, who reconcile the cost of the work conducted with the dealer on a monthly basis. This chap stated that around 30% of the work they did ended up in dispute with VW as the manufacturer felt the repairs were unnecessary; the dealer for their part was under pressure to fix a car for their customer and was at the "sharp end" with a reputation to maintain.
I don't know if Alfa run a similar process, but it wouldn't surprise me. It's a classic and familiar case of mis-aligned objectives for differing parts of large organisations; particularly when the dealerships are privately owned rather than by the manufacturer.
I distinctly got the impression that this was the case with my own Brera. When you chat to the staff in my local dealership, you can see that they believe you but have to walk the difficult line between that recognition, the reputation of their dealership overall and the attitude of the manufacturer. I actually have a lot of sympathy for the staff on the service desk!
Anyway, this was only an observation regarding the individual staff. I really hope this gets sorted as it's so frustrating when it happens and I thought I was at the beginning of a similar scenario myself.