I think they are behind Huawei in terms of development/delivery. As with all this stuff though, it's likely way more complicated than I will ever understand.
I raise a wry smile when Nokia are mentioned. Back in the day, when Nokia were the market leader in mobile phones, the network equipment side of the business was seen as a charity, employing lots of Finns to stop them appearing on the unemployment register. How times change.
What are the downsides to the others? Isn't it Nokia and Ericsson? Is it just they are more expensive?