Here's the thing, for me at least. It sounds better now. So at the end of the day, that's what matters to me. JP isn't a great singer - he can be decent, but that's about as far as it goes. MP wasn't a great singer either. In another thread we talked about James sounding good at a particular show in person, but not so good on recorded video from the same show. For me, the backing vocals (sometimes MP alone, sometimes both of them) made me cringe at the actual show. It occasionally took away from what was otherwise an amazing performance.
Personally, I do not think it sounds better now at all.
For one thing, I think that a live performance should, to the greatest extent possible, be LIVE. From that perspective, it sounded much better to me when all the backing vocals were being provided, *live on stage* by Mike and John, because I like to hear a live performance where it really does sounds like five people getting up and giving a performance, without any sort of assistance being piped in.
Additionally, I do not even think it typically sounds good on studio record when there are a ton of secondary vocal parts that are also done by the lead singer. It takes me out of the moment to realize that not only was the song not performed in a single take (which isn't such a big deal; few studio recordings are), but that it in a very obvious way could not have been so performed (more obvious than, say, an additional guitar track filling out the sound). And I think in most cases, where you even have a semi-competent backup singer, it sounds nicer to have multiple voices harmonizing or blending together than to have the same voice layered three times over. I think it's very cool when even bands with a very strong lead singer make use of the voices of other band members on the studio recording—e.g., Yes or Queen.
The liberal use of Mike and John as backup singers is one of the best things about the unfairly-maligned
Black Clouds & Silver Linings. I try to imagine the chorus of A Rite of Passage or A Nightmare to Remember with just three Jameses instead of James, Mike and John, and I just think it would sound, so, so inferior to the version we got—even though James is a far better singer than either of the others. By a similar token, I listen to something like Build Me Up, Break Me Down or The Bigger Picture and imagine how much better those choruses would sound if someone else was singing under James (in the case of BMU,BMD) or doing the secondary part (in the case of TBP).