Although agree with you on the most part, I actually wonder about their song writing ability. Given that almost all the songs they wrote when they were the Jacksons that were very good were written by Michael or co-written by him.
Also if they were such good song writers, they could of made a career out of writing songs for other artists. Sure it doesn't have the pay of actually performing the songs, but it better than the financial situation of many of the brothers.
In my personal opinion, the Jackson brothers all seems to be more glorified back-up singers to me. For all those fans that said Michael couldn't do it without his brothers is kind of like saying Smoky Robinson couldn't make it without The Miracles.
Even Michael's own mother said that Michael did not need his brother,s but his brothers needed him when CBS was trying to make Michael go solo before he was even out of high school and told his brothers to start looking for other jobs.
To be even more brutal, the people that Michael got to replace his brothers on those Jackson 5 songs actually sounded better than them in many cases.