Well. I have some experience with O2 too, from a customers point of view. Let me tell you a story:
Once upon a time i've been a happy customer of a regional ISP called Hansenet, started by the local public electric utility. It was (at least for me) lightyears ahead of the crappy experience (speed/latency/price/(competence of)service(if needed)) the former state monopolist had. Everything was golden, also excellent peering. They grew slowly, cooperated with some other regional upstarts, stayed golden, speed even got faster without raising of monthly fees, furthermore no long contracts necessary, could be canceled within a month.
Then Telecom Italia came and bought them, now it was Alice, as advertised by some mouthbreathing twen all over the public space, larger than life.
Quality of service went down, very unsexy of you, Alice!
But still was better than the former state monopolist, and still got faster without raising prices or contract conditions.
They even retained a local service center where you could walk into and talk to people who knew their stuff and could change settings in realtime! Imagine that! Not some outsourced call-center agent mouthpiecing some useless uml-diagram.
Anyways, too good to be true? Right! Telefonica came to rescue (of BlackRock), to milk the cash cow as long as possible, and it was noticable.
Fortunately another neighboring public utility, pioniering fiber roll out since the nineties expanded and became a choice for me then. All is golden again! Yay!
Why am i ranting? Because everybody i know is mostly unhappy with O2 in any form, except for the price.
O2 can't do!
I wish i could add some internal, even worse insights from another ISP growing larger at the time, but am not allowed to. Also they managed, got better, and meanwhile can do again.
Lesson? There is no lesson here, with the exception of economies of scale are bad for humans above certain amounts of 'scale'.