If I say in English "He's only playing" this can mean two things. It can mean something like he's just playing (and he keeps on doing so and it's bothering me because he should be working or something), or it can mean he's only playing (and that's all - what he is doing is harmless so don't be angry at him). The nuance is dependent on the tone.
Now, if I say in Japanese 彼は遊んでばかりいる, does this imply that I am angry at him for only playing? Or is the nuance that I am trivialising the fact that he is only playing and expressing it's harmlessness?