I could possibly count in one hand the number ghostwriters who broke through as solo artists. Koffi Olomidé was able to do it in 1978 with his successful singles (Synza, Anibo, Samba Samba, N'djoli, Cherie Lipasa ect). Macott de Katalas had a bit of success in the late 80s then flopped. Reddy Amisi and Felix Wazekwa would probably be the next 2 after Koffi as ghostwriters who became successful. I've seen the likes of Pascal Poba, Didier Mila, Benz Petrol, Do Akongo, Eldorado attempt but they've never went far. I've always been curious as to why

Great question that you ask. I can offer a theory behind two factors.
Either they did songwriting because they wanted to be known and get their songs exposed or those who tried to make it on their own get blocked by certain big artists.

i think most lack two three factors,sometimes they are not good singers so their work with proven stars is by far better,sometimes they have talent but lack of funds like do akongo,sometimes they lack the resilience you need like a wazekwa to make it to the top,it took him 5 albums to cement his status as a star while most writers abandon the dream if the first album is not a big success

It's already hard for former bandmembers themselves to breath through as solo-artists. We often tend to forget that 25 years he had only 4 solid-artists (Wemba, Koffi, JB and Werra) and the rest trying to surive or  to make it

I will not count Reddy Amisi. I see him more as a normal bandmember. Yes, he wrote some songs for Wemba, but than you will get a huge list of ghostwriters. Reddy Amisi himself was at some point Viva la Musica's N2 and did different tour on solo in Congo, when being part of Viva la Musica.

In Viva la Musica during the 1980s some singers and guitarists offered Wemba songs and if Wemba was interested he would put his name as auteur-compositeur, while the song normally isn't his. The same for Afrisa of Tabu Ley, were many songs were orginally written by singer Paul Ndombe. Another example is African Jazz where songs that got Grand Kalle's name as auteur-compositeur were orginally written by Izeidi, Tabu Ley, etc. More recent examples are Jules Kibens and Bogus Bompema with JB Mpiana and Serge Mabiala with Werrason.