Actually if I remember correctly this is the design used in certain comics (not sure if said comics were directly related to the game but I know they were set in the Old Republic era) so can't blame BioWare for this one. Actually if my impression of it all is right, the Republic Assault Ships from Ep 1-3 were made specifically for the Clone Trooper Army, not the Republic in general. The design of those ships and the clone trooper armor carried over when the Republic becomes the new Galactic Empire that we know in Ep 4-6.
Since the whole thing was one big plot (Order 66) made by Darth Sidious, I can't help but feel the design of the ships and trooper armor was intentionally based off older design, suggesting that design was the Sith Empire ships and Republic Trooper armor in the Old Republic era. The ships used in KOTOR were 300 years prior to SWTOR, so the triangular design could have been made during that time while the Sith Emperor was making his long term plans of returning the Sith to known galactic space. I could be mistaken and this is just baseless opinion, but it makes sense to me at least.
Since the whole thing was one big plot (Order 66) made by Darth Sidious, I can't help but feel the design of the ships and trooper armor was intentionally based off older design, suggesting that design was the Sith Empire ships and Republic Trooper armor in the Old Republic era. The ships used in KOTOR were 300 years prior to SWTOR, so the triangular design could have been made during that time while the Sith Emperor was making his long term plans of returning the Sith to known galactic space. I could be mistaken and this is just baseless opinion, but it makes sense to me at least.