I do think Altair, Ezio and Connor would be mortified by the concept of Animus but At first they would probobly think that its funny, like Ezio would be going "so you just lie down, watch us go about and wake up with our skills?.... Thats cheating!!!" Altair would be prob a bit salty. Connor would wish he had that of an easy time training.
Then they learn its not like "lying down and resting while animus does the work" at all;
Desmond wakes w muscle spasms and phantom pains from injuries he never got. He has chronic insomnia because his sense of time has been blinded so much he is basically jetlagged 24/7. He doesnt remember how long a day is supossed to go, how slow a month passes, how decades indeed take decades. He has backpain from lying down all day without being able to move, then his muscles protest when he has to move out of animus because thats the only time he used them. He forgets to eat, sit, drink, shower till someone tells him because he didnt have to in animus. He is shocked when people speak to him unprompted because there was always a reason for someone to talk to him first in animus.
Then they learn about his bleeds, how he became a puzzle of their skillset but also their minds. How he forgets his likes and dislikes because he has been others daily, longer than he has been himself in a while. He forgets where he is, if he is supossed to be there, if what he is seeing is supossed to be there. He forgets his name sometimes, replies to anything but his own even if the person is in the room as well. How he freaks out when he sees his reflection sometimes, remembering it as a strangers face. How he sees and talks to things that arent there but maybe was or will be.
They learn he isnt even himself sometimes, cant remember how to be. He doesnt know if he is mad at someone because he doesnt like them or if its Others feelings bleeding. They learn some of his own memories been forever replaced by their own and he doesnt even realize he never met that person only Connor has met before. He cant remember the day his mom got him his 5th birthday gift but Ezio's 5th birthday and his new gift of a carved horse figure is fresh in his mind. He doesnt remember his girlfriend from when he was 19 but he remembers Altaïr's one crush that lasted a week. He cant remember if he ever tried a dish but knows if one of them would like it based on the ingridients. He cant remember faces of his classmates at the farm but knows the novices names by heart.
They learn while they might have sacrificed their bodies and years for their training Desmond has sacrificed his whole self for it.
And it doesnt seem like cheating anymore.
