In TG7 the Murasaki effect is said to encompass four solar systems. It's unlikely you're going to get far in something that big without warpdrive.
True - but the expedition apparently didn't try to reach any of these systems originally, nor actually enter the effect.
The existence of a warp drive aboard the TOS shuttles was seldom in question. The viability of that drive for interstellar runs was much more rarely suggested. "The Galileo Seven" is just about the only case where this is implied, and only indirectly: any single of the systems could have been very close to the starting point, but for more than one to be within range means the range is truly interstellar. That is, unless the systems within the effect were as anomalious as the effect...
A bit curiously, TOS still remains free of cases where shuttles would have explicitly been in transit from one star to another, even if the capacity was suggested.
In "Metamorphosis" the shuttlecraft wouldn't have been so hard to track down if it wasn't so far away in the first place, and without warpdrive the shuttlecraft is useless as the E could have picked up Commissioner Hedford on its own much faster.
But we know for a fact that a shuttle can't catch a starship even when moving suicidally fast, as per "The Menagerie". The reason the ship wasn't used for a direct pickup in "Metamorphosis" thus has to be something else - such as the asteroid belt explicitly mentioned in the episode, a belt no doubt better navigable by (low warp) shuttle than by starship.
Although it was never explicitly stated in TOS that shuttlecraft did or didn't have warpdrive I suspect the writers didn't really think it through and/or didn't really appreciate how BIG space really is.
OTOH, I'd think they treated the shuttles like they would treat boats, vis-á-vis ships. It would be one for the history books if a boat made transoceanic transit - and while Captain Bligh makes for a good story as such, it may not be particularly suited for the Trek format.
And this project doesn't acknowledge whatever was done in TNG, DS9, VOY and particularly ENT since they're irrelevant to and inconsistent with TOS.
I'm not sure the distinction is particularly useful. After all, TOS was inconsistent with TOS, typically far more so than the spinoffs were with themselves, with each other, or with TOS.
Timo Saloniemi