Well?
U2 are still a rock band like they were when they first started. This term "Dad Rock" is meaningless because it has multiple definitions many of which contradict each other. If you don't fit into the narrow box of what some perceive as indie'/alternative rock, then you could be tagged with the label.
When you think about it, any definition of anything is subjective, relative and culturally situated. Additionally, definitions vary over time. A band like Radiohead, for example, could neatly fall under the definition of ‘rock’ up to, and including, The Bends. OK Computer could usefully be considered ‘art rock’. On the other hand, an album like Kid A falls more neatly into the category of ‘electronica’.
U2, since POP could, depending on the song, accurately be defined as ‘rock’, ‘pop rock’, ‘soft rock’, ‘dad rock’ or simply, ‘shite’.
While most people would tend to agree, to a certain extent, on what terms like Heavy Metal, Hard Rock, Rock, Pop, mean, with "Dad Rock" it is far less clear with nearly everyone having a different definition.
If "Dad Rock" is music one does not like, then U2 are definitely not Dad Rock, because everyone here likes U2.
You can do better than this, wons. For example, ‘most people’ cannot agree on what heavy metal is. Are black sabbath ‘heavy metal’? For me, like Led Zeppelin, they are a blues based heavy rock band. Are van haylan ‘metal’, ‘hair metal’, ‘hard rock’, ‘puerile idiots’ or simply shite? Each definition divides itself up into multiple sub categories.
The Oxford dictionary defines ‘Dad rock’ as ‘music that appeals to the older generation’. Which, let’s face it, is exactly what U2 do now.
So, if Oxford University can come up with a clear definition, that’s good enough for me.