someone said train and lady a were one hit wonders. In that case:

Beyonce
Michael Jackson
Britney spears
Lady gaga
Whitney houston
Usher
Rihanna.

Nowadays anyone can get at least one more hit after their debut, but their album flops and their singles will slump next year.

This is for this year.. so yeah,
Lady Antebellum only had 'Need You Now' as a hit song, the rest either flopped or weren't really popular.
Train, this year, did not.. they had 'Hey, Soul Sister' and 'If It's Love' did decent.

That's like calling Hayley a one hit wonder if she goes solo when technically people already think she IS Paramore.

Most of these examples havent even released a second single too even be considered a 1 Hit Wonder.

Lady A is on the hot 100 right now and they had a few strong singles but they weren't taken
up by pop radio more country.

All four singles from Lady Antebellum's album charted on Hot 100 (Need You Now, American Honey, Our Kind of Love, & Hello World). Hello World is doing that well currently, but it's still charting. And yeah Train has had three songs from Save Me, San Francisco charted on the Hot 100 (Hey, Soul Sister, If It's Love, & Marry Me) and might get a fourth soon(Shake Up Christmas).

Now I would like to now; do you guys mean one hit wonder on pop radio or overall?

You need to be in the hot 100 to be considered a hit? Even if your song is at #100?
I thought your single had to go top 40 to be considered a hit.. so that means Train would have 2.. and I don't remember any of Lady A's other singles going top 40.