Another way of looking at it is that there's about a 15% dimensional difference on the scales.
You get into trouble because all three dimensional objects follow the law of cubes.
So 1.15 (the length of a 1/350 aircraft divided by the length of a 1/400 aircraft) times 1.15 (same math for width) times 1.15 (same math for height) gets you an overall volume increase of 1.52, or 50% larger in bulk. To me that's a really big deal.
You'll find those a/c. I gave you the name of L'Arsenal which has a lot of 1/400 stuff, but there are other sources too.