Perhaps a better solution would be for a newly started node to obtain its transaction pool from its peers?
[...]
So I have to ask why was this feature implemented in this manner?
Without saving the sync would be a _massive_ waste of bandwidth, so it was important that the saving be done first. The two are complementary.
Saving was also substantially driven by the motivation of being able to save prioritization for miners; which is not accomplished via syncing.
Saving is purely a client local feature-- it's something the Core project can decide to do without worrying if other implementations like it (and, in fact, Jeff Garzik showed up out of nowhere, having not sent a single message to the project in months, and attacked the saving vigorously)... syncing, especially efficiently, requires a BIP and collaboration with other implementations some of which are hostile to the project and reliably oppose every proposal. So it didn't make sense to hold up the saving for the syncing to be worked out, since saving really is no other implementation's business.
Efficient syncing is also an
active area of research, there are techniques to perform the sync in ways which are significantly more efficient than you might guess. (But, of course, if you throw out the data-- it's going to have to be transferred again, saving it is the only way to avoid that!)
The file is only written at clean closedown, so it is of limited use during an unexpected system failure
An earlier version of the proposal did periodic flushes, but we're concerned with creating excessive writes that lower the lifetime of SSD, and having half completed write can be worse than no write since we'll lose the in-progress flush. The ability to trigger a flush via an RPC will probably come back, so if you want a periodic flush you'll be able to crontab it.
This feature is pretty much useful only for virtually immediate restarts.
Not entirely, it's also useful to pick up some low feerate stuff that otherwise wouldn't be mined for hours or days... so even if you were off for a few hours it can have value. If you're off for weeks it would be worthless, however.
Saving also improves the accuracy of data for long term fee estimation.