The SVL file actually supports Circles or arcs only in either the 3D linework or Design Map data output. In the other output it only supports a chorded approximation of the circle or arc. I apologize but I cannot tell which is which because if you select one it also exports the other (i.e. both) and it doesn't differentiate between the 2 in TBC after Import again so it is impossible to tell which one drives which output - My guess is that the Design Map outputs the Circle and the 3D Linework output is chorded (because the Site Map Export Option outputs a Circle (and that also supports a DXF file which makes sense).
The chorded version of the lines are chorded on Export using the settings in Project Settings for Surface Computations for Breakline Approximation Parameters as shown below
The default was changed when we moved to TBC v5 onwards and is likely set to 0.05' compared to 0.02' in v4.12 of BC-HCE. This will create less chords on Arcs / Circles than in BC-HCE 4.12. Either way they would both have been chorded as that has not changed for many years. Try change the settings in your Source project to 0.02, 0.02 and 10' and then output the SVL again and then reimport it, that will likely fix the issue.
Here is what I see when I output an SVL file of Design Map Linework and 3D Linework using a tolerance of 0.02' - the blue dots are the chord points
zoomed in it looks like this
The Orange line is the Circle - the black line is the chorded approximation using the 0.02' tolerance.
When I use a setting of 0.05' this is what I get
as you can see less than half the number of chords
And zoomed in it looks like this
You can see that the Arc and Chord separation is greater here )that is the 0.05' distance).
Hope that this answers the question
Alan