I didn't write "all", I wrote "most"! And in view of the requestor and his project, note that I'm not sure that there were any British AdCs over the rank of colonel, and they were few and far between. My post of March 2007 was in response to Art M.'s question about British AdCs, and those in the Peninsula were mostly lieutenants and captains.
Consider Britain's "General Regulations" (1811; p.29):
Regulations to be observed in the Appointment of Officers to serve upon the Staff of the Army, and in their Removal therefrom.
No Officer shall be allowed to fill any Staff Appointment (that of Aide-de-Camp excepted) until he has been four Years in the Service.
No Subaltern Officer shall be considered eligible to - hold the Appointment of Aide-de-Camp, until he has been present with his Regiment at least One Year.
Aides-de-Camp (except those attending His Majesty and theCommander-in-Chief) must not be effective Field Officers of Regiments.
No Officer under the Rank of Captain is eligible to hold the Situation of a Major of Brigade, nor must effective Field Officers of Regiments be employed as Majors of Brigade, or as Fort or Town Majors.
Officers for the Staff of the Army are to be selected exclusively from the Regular Forces, and no Regiment of Cavalry, or Battalion of Infantry, shall be required to furnish more than two Captains and two Subalterns for Staff Situations.
You can see that the bulk of AdCs was expected to be drawn from among subalterns and captains, while regimental majors and lt-colonels were generally barred from the job!
And in March 2007, I had referenced, also, Charles James' "Military Dictionary" (1810) :
"AIDE-DE-CAMP, an officer appointee to attend a general officer, in the field, in winter quarters, and in garrison; he receives and carries the orders, as occasion requires. He is seldom under the degree of a captain, and all aides-de-camp have 10s[hillings]. a day allowed for their duty. This employment is of greater importance than is generally believed: it is, however, often entrusted to young officers of little experience, and of as little capacity; but in most foreign services they give great attention to this article. Marshal de Puysegur mentions the loss of a battle through the incapacity of an aide-de-camp. The king may appoint for himself as many as he pleases, which appointment gives the rank of colonel in the army. Generals, being field marshals, have four, lieutenant generals two, major generals one, and brigadier generals one brigade major [who is not an aide-de-camp, but attached to the brigade rather than the brigade commander]."
Art's question was, I think, focused on Britain's practice, and I answered it with that in mind. But I acknowledge that you are quite right: in other services, like France's or Russia's, a number of AdCs for high-level general officers or marshals held high rank.
Cheers - Howie