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It's mainly just the persistent use of barely-finished stamped and folded metal for the outer clasp and the fold-over security catch. As a diver's watch, a bit of bulk isn't surprising when they're going for strength & durability and have a fold-over extension in there as well. It just kind of lets the rest of the watch down in terms of finishing.
Just get it on, or put it on, a rubber strap and all's fine.
Bracelet clasps are a major major Seiko weak point on anything below GS level. Just like the Turtle, I don't think that case style ever really looks right on a bracelet anyway, but IMO they're really starting to push their luck at the price points these new 6R divers are reaching. You can kind of accept it at £300, not so much >£1k.