Given that Vulcan's PD info from Captain's Log implies that service with the Science Academy is promoted to a relatively high standard (compared to service in Star Fleet) than on other major member worlds with their 'legacy' fleets, it might make sense for Vulcan to be somewhat more reluctant to give up its own ships at the same time as others.
Plus, they still have the use of ship-mounted phaser-1s and special sensors, which even Star Fleet couldn't get right until the mid-2520s or so.
Early Years Question
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