Longest Reach crafted 1h and 2h swords are the same length.

[BoogieMan]

Choosing the blades with the longest reach and scaling them up as long as possible for both one-handed and two-handed sword results in a sword of almost the same length.

 

[NordicNoodle]

You can make really long one-handed swords. A big difference comes also from the handle. And from some testing I feel like you are right. The two-handed swords dont scale as much up as the one-handed. Both have about the same max. length (around max. 125). The stats are quiet different though (the two handers have up to 130 cut dmg).

 

[jakl201]

I have seen some swords that can switch between one handed holds and two hands, might be tied to the hilt used. Unsure about which parts will allow you to switch between the two modes. Smithing still needs to expand info it gives you.