I share a lot of the disappointment of the community over the size. My first choice would have been a much much smaller size, with squads of troops on stands and multiple AT-AT sized vehicles in every battle. But that is because I like that scale (and I love AT-ATs). Failing that I liked the idea of being able to share minitures between IA a SW:L, but then I have never really played IA.
And that brings me to why the slightly larger minis might be a good thing. I have been tempted to get into Imperial Assault for a while. But my temptation for X-wing and Aramda latterly lasted nano-seconds. In truth I was super impatient for them to come out. Two of he reasons why I wasn't as excited for IA were obviously because the game just didn't appeal to me as much and because I was already invested in two games that where stretching my resources. That being said I think the minis themselves might have been a third reason. Everytime I looked at the IA minnis, they were cool because they were a Storm Trooper, or a Jedi, in other words I liked them because they were minis of things I loved from the Star Wars Univers, but I never really loved the minis themselves. I'm not saying they were bad, they just weren't enough to get me excited about. And this brings me to my point I really like the Legion Minis. I think giving them a little more size (and letting them be minis that need to be assembled) we got cooler minis. The difference isn't huge, but small things can make a difference between cool and not as cool.
I conclusion, while I am a little frustrated with the size choice FFG made for Legion, if it means the minis are just better then maybe just maybe it was the right choice.