The Bears are the only Clan that doesn't use the phenotype at all, but we don't know how much other Clans actually use them.
As a percentage of their trueborn pilots. I suppose I can't really argue with your headcanon. So, I'm not going to bother. I'm sure some funky examples to the contrary exist somewhere. I recall the Goliath Scorpion loremaster in FM: WC being described as uncommonly tall for a pilot. Yet even in that description it reads like this person is abnormal.
In creating Clan characters for stories and RPG-style games, I've definitely created some variations on the aero phenotype just because I wanted characters that looked more average human (or I wanted to use a particular real world person as the image for that character and they didn't fit the aero description very well), often fluffed per my non-canon wishes as things like "a warrior from an experimental pilot sibko" that perhaps had some of the aerospace pilot traits but not all of them. But it's all purely my non-canon funzies.
Yet that non-canon fun stuff does also provide some rationale for some pilots to be out there who don't quite fit the phenotype mold.
But as we were discussing the Wolves specifically, we know they used it plenty. Carew aside, in the Clan Wolf Sourcebook there are specific named/described pilots, I believe a named Star Commander and Star Captain described as being of the phenotype. Even if they don't say "phenotype" they describe big heads, big eyes, and slender physiques. They also use phrasing like how that physique is common of "all" or "many" aerospace pilots. It was really through the early Clan Wolf-centric products like the Blood of Kerensky trilogy and the Clan Wolf sourcebook that the idea that Clan pilots looked this way was introduced to the player base.
Circling to the real point, I suspect Metallgetwitter has it right. I think the Crusader Clan had a shortage of bodies. As of FM: CC they were pulling every potential warrior they could find from anywhere. They were giving failed Trueborns of any age another chance against garrison-level opponents to rejoin the touman. They were drafting members of the lower castes who showed aptitude. In the novel that depicts Vlad Ward becoming the Khan of a resurrected Clan Wolf, it talks about him pulling warriors from non-warrior duties like sibko instructors, and how that would be problematic in some ways, but he just needed bodies right now to rebuild the Clan's touman before another Clan decided they were easy prey.
That's the explanation that makes the most sense to me and fits the evidence. Most-to-all of the Clans were using failed aerospace pilot phenotype individuals as their first ProtoMech pilots. They had an excess of bodies and they used them for that, in the process that represented that individual's opportunity to remain in or return to the warrior caste. The Crusader Wolves had no such excess. Anyone that fit that description that had any warrior aptitude at all was already being sucked back into the touman already. Excess bodies was a luxury Clan Wolf didn't have.
That thought was already floating around my mind when I started this thread. But I wanted to see if anything canon existed on the subject.
