As mentioned there is no difference between S shape and straight arms as far as the alignmnet at the nulls and the arc described across the record. The angle of the S is usually similar to the offset angle on a straight arm.

Linear tracking arms are not all actively driven. Most linear trackers are not driven. eg Air Tangent, tri-quartz. I believe radio shack had an active linear arm in the seventies.

Having a longer arm will not make overhang adjustment easier, sliding the cartridge in the mounting slots is about the same in both cases, as is the the overhang. Overhang is the distance the arc of the stylus extends past the spindle.

Unipivots misalign on large excursions? Maybe on a severely warped record but not due to groove modulation. There is not enough vertical motion following a groove to misalign the stylus signifigantly.

I used a Linn for over 10 years and while it's not my favorite table, mine never ran slow. I would have that looked at.

I know this sounds somewhat more negative than the usual for this board but some of your info seems incorrect.