The 6L35 appears to be a mix of the 4L25 and 4L75 as it has the power reserve of the 4L25 (45 hours), but the accuracy of the 4L75 (+15/-10 sec) rather than the 4L25 which was slightly less well adjusted. This helps to explain the rather high pricing of this Presage which really is more in line with the pricing of the Credors powered previously by the 4L75.
Why then did Seiko make an imperfect clone of the 4L given that all the fundamental specifications of the movement are the same? I suspect that this was due to the licencing arrangement between Soprod and Seiko regarding the 4L and Seiko had to work around this by changing, cosmetically, certain parts of the 6L including the balance wheel and anti-shock system in order to avoid infringing their agreement with Soprod.
This then brings us to the next question of why Seiko had to bring back the 4L caliber to power its new Presage models.
Firstly, as many people have correctly noted, Seiko movements are generally never thin. For example, all modern GS are at least 13mm thick. Having the 3.6mm thick 6L movement would allow Seiko to introduce true thin dress watches below 10mm and better compete with its European counterparts.
Secondly and more importantly, Seiko likely made a huge expense in designing and manufacturing the 4L family, and it was only used in models from 2007 – 2008, with it then being relegated to the Credors until 2013. Seiko probably had to recoup the capital it invested in building the machines to manufacture the 4L family, and was waiting for the right opportunity to utilise the 4L movements in watches that could fetch a higher price. After all, it’s pretty telling that the 4L/6L is the first ever movement that went from an upper tier line (Credor) to a lower tier line (Presage). Every other movement generally stayed within its own price bucket/line, with the exception of the Seiko 4S, which moved upward to power the Credor from its pedestrian origins powering the normal Seiko mechanical timepieces.
The time is now right for Seiko to introduce ever higher priced watches that do not carry the GS designation which requires manpower intensive work in adjusting and then certifying each and every watch. By introducing the 6L powered Presage (probably the most expensive time only Presage ever), Seiko could hope to recover some of the investment made in its movement, while getting consumers used to ever higher price points in the Presage range. This would then allow Seiko to creep the price points of its top tier Credor and Grand Seiko lines upwards as well.
Cal. 6L35 is a high-end slim automatic movement with date from Seiko. Produced only in 2018, it part of the earlier Seiko 4L/6L family which provided the design for the Soprod A10 family of Swiss movements. It is exactly the same size as the popular ETA 2892A2, and has similar specifications as well, though the design is completely different. It is similar to Cal. 4L25 and 4L75.