I'm not sure I follow; why would it be lesser in ATL?
The Arabo-Islamic conquest unified, first politically, then culturally/economically northern Berber peoples/states/cities.
For the first time, Mediterranean markets and Sahelian producers were directly tied, and participated to a global trade structure (similar coinage, trade rules or even tools of the trade as camels that were widely used in the region after the conquest).
It allowed easier exchanges whom the main was slave-trade (the need of servile taskforce of Arabo-Islamic states was certainly important for the flourusing of trans-sahelian roads). Without an economical continuum that passes trough North Africa, it's likely that they won't participate as much as they did, unless someone else took the part of the conquerors, but I think it's unlikely.
I'm not sure I follow this either. What would make Africa different from the Baltic, the Rus, or Eastern Europe? Christianization and the development of state structures happened everywhere around Europe.
Well, these are different cases.
Eastern Europe and Rus' basically are due to the Byzantine policy to create clients, or at least allies; and to the economical/cultural influence of the empire.
Without political motivation to do so (as it existed IOTL with Maur Kingdoms bordering Byzantine holdings in Africa) and without byzantine focus on trans-sahelian trade, I doubt it would appear quickly.
As for Baltics, we're largely in a crusade-context associated with political interests. Considering Crusades themselves
are so tied to Islam that it's probably butterflied as such ITTL, you may still see expeditions as Charlemagne's against Saxons, but there's again political concerns existed as well.
What would be the political motivation for Byzantines to undergo what would be a ruinous expedition in North Africa (which is mandatory before going for sub-saharian Africa)? IOTL, they had trouble enough stabilizing the border between Africa and Maurs, and more or less disinterested from the province after a while.
Goths may have better reasons, but they wouldn't be able to enforce these for what can be forseen.
Not that I'm saying Christianisation of West Africa wouldn't be possible : it just doesn't strike me as obvious ITTL, for what matter immediate consequences of the PoD.
EDIT : Please note I'm talking of West Africa. You didn't mentioned it in your OP, but relations existed with East Africa, and may continue to flourish. The lack of the aformentioned continuum wouldn't be that problematic, critically with Roman and/or Persian presence in the region that may lead to conversions.
I'd say that you'd have better chance having important states or peoples in Eastern Africa : Horn, Somali, Great Lakes, Zimbabwe, etc.