Steel tube comes in a variety of diameters and thicknesses. Titanium much less so. Thus, a titanium custom builder has fewer choices of his raw material (tubes) from which to customize. This may, or may not, make a difference in any individual case. Depends. But you can be sure the that the Ti maker will make no mention of it.

The whole thing about non-round Ti tubes (rejected by most steel frame makers several decades ago) is a jury-rig to get around the lack of tube selection.

Kind of like the straight jacket that lugs present compared to welded tubes. I know some point to strength issues but, ignoring or disagreeing with that, lugs do put one's geometry in a straight jacket compared to welding custom steel frames.

For the record, I have both steel and titanium frames (but none of my steel frames have lugs), all of which have nifty carbon parts like forks and such.