I am in a good position to answer the OPs question regarding AT versus 250 Rally, as I have both.
First me, age 67, ridden since age 16. Too many bikes to list but all large capacity. Dont ride in winter due to salt. six foot 5 so need a tall bike.
March 2018 bought the ATAS, loved it and still do really. Lovely looking bike. Giving up riding from October to April was getting me down so I decided to buy a cheap bike to ride through winter on those cold sunny days . In the end I bought a new Rally. The idea was I would wash it after every ride and if it corroded a bit so what I still had my mint ATAS.
So how did I get on with the Rally after so many years on big bikes. My first impression was hey, no power, vans want to overtake me. Then I started to ride on small roads that I have avoided all these years. The lightness of the bike was great. I started to really really love the rally as it changed my riding completely. I found places I didnt know existed. I get 90mpg. It costs nothing to insure. Its a doddle to work on. I have added extras and modified suspension and I feel a bond with it that I dont feel on the AT
The biggest difference for me is the weight. The ATAS is tall and carries its weight high. By comparison the rally is a toy - a nice looking toy. If I had to give up one of the bikes it would be the ATAS. As I have room for both I will keep both. So far this year I have done twice as many rides on the rally than ATAS. So to conclude, the ATAS and Rally are totally different. In theory the ATAS will do what the rally will but you have to work at the slow bits. The Rally is a hoot to ride on smaller roads and changes your attitude to riding if you come from big bikes. If you dont want speed/distance its the rally.
The rally will most likely be my next bike. My oldest son will be getting one for his first bike. He's only ever ridden my crf230l, and while he's be fine on a cb500x or nc700x, after trying several, he prefers the slimmer machine.
He's 6'4" so he really needs something taller than my 230l. As for me, I just want to add a rally for a taller, lighter weight economical bike. I like motorcycles, so sue me😁