Similarly, a recent opinion piece in La Libre (https://www.lalibre.be/debats/opinions/non-leopold-ii-n-est-pas-un-genocidaire-567922033570ed3894b6608a) refers to the Commission d’Enquête of 1904-1905, which (according to the author) is widely considered to have been an unbiased and an independent commission, which concluded that "the white man" [sic] never inflicted such mutilation on living indigenous peoples.

That opinion piece is misleading in several particular details, and not representative of current academic consensus regarding abuses in the Congo Free State.

To directly answer your question about the Commission of Inquiry of 1904-05 (or Commission d'Enquete in French), it was a commission appointed by Leopold II in response to pressure from the Congo Reform Association. The commission was remarkable because its report confirmed accusations of abuses, rather than white-washing the whole situation.

However, when we read the report, particularly the chapter about military expeditions, the report gives (frankly racist) explanation that blames the Congolese foot-soldiers of the Force Publique for every instance of atrocity. Statements like the following [trigger warning for racism]:

The instructions of the Government fix the rules to be followed in all police operations and consequently those that should serve as guide in those expeditions which have for their purpose the compelling of natives to acquit themselves of the imposts

(that is to say, a Force Publique patrol to demand rubber quota)

Often expeditions of this sort consist simply of a reconnaisance, a peaceful trip, during which the white officer, obedient to the instructions quoted, does nothing more than lead his troop into the refractory of delinquent village. He place himself in touch with the chiefs, showing the blacks, who respect nothing but force, the power of the State and thus proving to them the folly of an obstinate attitude that would bring them in conflict with the State. This method of procedure has often had excellent results.

It is perfectly right that in the course of this expedition that the troops should arrest the delinquents in order to coerce them in accordance with the law.

Unfortunately the expedition did not at all times have this specific character and its good effect. Sometimes it has been deemed necessary to act more energetically.

In these cases the order issued by the superior officer to the commanding officer of the expedition usually instructed him to "remind the natives of their duties."

The vague generalities of such orders, and in certain cases, the thoughtlessness of the one to who is charged their execution have frequently had as a consequence unjustifiable loss of life.

However, it should be understood that the task of the officers to whom such missions are confided is the most delicate and most difficult.

It most frequently happens that the natives flee at the approach of the troops without offering any resistance. The Tactics generally followed consisted then in the occupation of the abandoned village or the plantations which are near by. Driven by hunger the native return either singly or in small groups. They are arrested and compelled to surrender the chiefs or the important men who, nearly alway,s submit, promising never again to fail in their obligations, and sometimes in addition are required to pay a fine. But it sometimes happens that the natives return slowly. One of the plans usually followed in such cases is to send out search parties and beat the bush, with instructions to bring such natives as they may find. The dangers system are easily seen. The armed black left to himself feels the recurrence of the sanguinary instinct which the strictest discipline is scarcely able to restrain. It is during this service that most of the murders are committed that are ascribed to the State....

[from pp 88-90, emphasis mine]. Through that excerpt, I hope it is clear that the general tone of the report tries to present a picture of "a few bad apples" among officers, or racist caricatures of "warlike nature" of the Force Publique foot-soldiers, while the authors seem unable to comprehend the euphemism of orders to "teach them a lesson".

So, for that reason, I think we should read claims that "The white man has never inflicted or caused to be inflicted, as a punishment, for breach of services or for any other reason, such mutilation to living natives" as a claim circumscribed by the general tone of the report, which seeks to explain abuses as either a break-down in discipline or the manifestation of savage nature of Congolese foot-soldiers.

In short, the authors of the report believed in racial hierarchy, believed in the civilizing mission of colonialism, and did not question the right of the Congo Free State to 'chastise rebellious villages' that failed to make rubber quota. Yet this report still had to admit that atrocities were committed.

So, Mr la Motte's talking-up the commission's "unbiased" nature is very misleading.

Hence, my earnest question in the title: were the Belgian colonies more cruel than other colonies in the same time period, or are these injustices exaggerated (comparatively speaking)?

Yes, other European powers engaged in brutal practices in their colonies. There were schemes of coerced labor in mines, plantations, public works (railroads, roads, military installations), porterage; in British colonies of Kenya, Gold Coast, Nigeria, North and South Rhodesia. French colonies like Moyen Congo and Soudan (now Mali) had forced relocation and forced labor in cotton growing schemes, rubber plantations and railroad construction.

During the Boer War (1899-1902), the British army constructed internment camps that held Boer civilians as well as black South African populations in dire conditions. (Popular memory tends only to remember the suffering of Boer civilians in these camps). Mohandas K. Gandhi would later remember the Bambatha Rebellion (1906) in South Africa as a situation where white British soldiers and officers hunted down rebels for sport.

The Germans infamously conducted a genocide against resistant Nama and Herero populations circa 1904-1908 in what is now Namibia by forcibly relocating them to the Namib desert and allowing populations to starve. In German East Africa (now Tanzania) in 1905-1910 there was a brutal counterinsurgency campaign against the Maji-Maji rebellion, followed by drought, famine and demographic declines in the southern third of the colony.

The violence of French conquest of West Africa in the 1880s produced it's own scandal and that military conquest was maybe comparable in it's violence to the initial conquest of the Congo Free State or the Congo-Arab wars.

Yes, there was an enormous amount of violence, brutality and coercion that happened in the colonies of the other European powers in Africa.

But Congo Free States atrocities were not exaggerated. And the fact that the British and French and Portuguese and Germans were all horrible does not excuse Leopold II or the European agents (not all Belgian!) who had roles in the Congo Free State. In the same way as Mao Zedong's Great Leap Forward and Stalin's purges do not diminish the crime of the Holocaust.