Short answer: very objectionable
Circumstantial and personal considerations: I find it appalling to insist any being into that form of life style, sentience and intelligence aside: i.e. even if Yeerks were okay keeping horse bodies, it's not okay to do that do the horse.
I still a yet to have an acceptable source on the origins of sentience: is someone born sentient? Is sentience itself an instinct? Must you develop it via experience, or is it merely expressed at a certain stage in life, like some more notable physical features?
Applegate doesn't do a great job detailing it's place in morph IMO: is it absent in a morph, or manifest in that suppression of other instincts?
It seemed to me that a morph human/andalite/whatever may not have had the memories and knowledge of the original, but was it non-sentient? Harder to say.
Re: growing thing, even if you have to grow into sentience: Other morphs seem to do fine if the morpher submits to the forms instincts, why would a sentient being be any different? Instinct is like sentience in this some sense; where does it come from, what shapes it, how much of it is retained in the form. If a croc from DNA alone can figure to attack a bear off the bat, I figure an adult human of DNA could figure to run away from a charging bull, or something.
That in mind, original's loss of identity, what about clones? Even if the original consents, if the clone can have it's own mind, it still is basically seeing it's own body relegated to that hell. And I wouldn't say that the clone is one's to give away any more than a set of parent's should be able to say "we'll have a baby just so it can group up to be a host"
Personally I didn't like the Iskoot's methods. One I'm not clear how it works, and two generating a creature to be a dependent vessel on another, even if reciprocated, still off putting to me.
Creature, no, machine yes. Build some more Chee (weaker Chee) let a yeerk control it for a life time, then be on with the day
And because I looked at the original post
Ah thanks! I must have missed or forgotten that. Okay in which case acquire the leading athletes in their respective fields. You've got yourself a super soldier, the best of the best.
If I'm understanding correctly, with fastest man and most durable man for example- you wouldn't get a super solider who can sprint for 5 hours. Form and function for being excellent in one area negates the ability to excel in an opposing one. More example: A is 100% red muscle (great endurance) B is 100% white muscle (super fast). Mixing them gives you a C 50/50 red and white, not 100% red and another 100% white. C is faster than A, but slower than B, not as fast as B and as durable as A. Trade offs.
At best you'd end up with the best person in the world at being AVERGE.
If you mean tops in a single field though, fastest and second fastest, well, maybe it compounds, but I don't see how.