From the thesis of the former Prime Minister of Ethiopia, the late Meles Zenawi:

"The political and economic renaissance of Africa is an issue that continues to preoccupy Africans' and non-Africans alike. Various methods of achieving such a renaissance have been proposed.
Most of these proposals are variations of the dominant neo-liberal paradigm of development. My argument is that the neo-liberal paradigm is a dead end, is incapable of bringing about the African renaissance, and that a fundamental shift in paradigm is required to bring about the African renaissance."
Another section
"Creating the proper blend of norms, values and rules to reduce uncertainty and transaction costs is a critical factor in accelerated growth and development. The creation of such social values and norms is called social development or social capital accumulation. Social development is thus not only an essential element of development but also a critical instrument of accelerated economic growth.
The accumulation of social capital, which plays such a critical role in accelerating economic growth, is a public good which has increasing returns to scale. It is, hence, undersupplied by the market and is subject to vicious and virtuous cycles. It is created by social activity by civic engagement in the context of horizontal and dense networks and inculcated and sustained through modeling, socialization and sanctions. The state plays a critical role in social capital accumulation through undermining patronage networks and promotion of fairness and equity, through the promotion of participation and democracy, and through appropriate sanctions and efforts at socialization."

Document is titled Dead Ends and New Beginnings

A lot of big sounding words, but basically, he says when a country is developing from a very low level like Kenya and most other African countries, the state has a big role to play in guiding development and allocation of scarce resources for maximum return in the best interest of the country. However, the state has to do it right. Not be wasteful,corrupt and inefficient.

Your definition of GDP makes me wonder whether we should really be having this arguement. Where did you get that definition, this is what the internet searches give:
"Gross domestic product (GDP) is the market value of all officially recognized final goods and services produced within a country in a given period of time"
Back to the Kenya Vs Ethiopia debate, It can be argued that Ethiopia has more potential at this point due to better endowment with natural resources, however, for me I look at just 1 item that Kenya has and that is human capital, this is what has built America and Japan and UK, Germany and now India.
Ethiopia is like russia while Kenya could be like Germany in the African context, who do you think has more upside.

On the businessman saying Ethiopia has more potential, one needs to look at the context he was observing this, for a business mind, your interest is profits and not development, Ethiopia currently remains greatly under exploited, therefore its normal for a businessman to look at the markets where he will have less competition, make higher returns etc.

Finally, the overall size of the GDP is irrelevant, China may have a larger economy than say Taiwan and South Korea, but it will take a very long time to catch up with either of this two countries on the all important number of GDP per Capita, which is the more important indicator. Ethiopia with twice Kenya's population should certainly have a larger GDP and present a more juicier market, but that does not mean they will be more successful than us.