I'm afraid that Colossus is indeed on a smaller scale, even with other X-Men from DST. It is indeed sad that there is no extra care to keep the statues from the same line (Marvel Premier) a constant scale. I know I can return it if I'm not satisfied, but this shouldn't be a business principle.
On another note, I have seen some complaints that Colossus is arriving damaged. Not broken, but rather with poor glue application on its parts.
Mine has arrived separated by the waist. Glue was applied on two flat surfaces, which is half way through for the glue not to adhere properly.
Given how heavy the Sentinel is, I was kinda happy mine has arrived this way, because I was able to reinforce it. Sadly, I believe some people may find this problem the hard way, because the weight of the Sentinel may start to cause stress on the waist.