In Hardcore, i would say its more dangerous to get a boost then to slowly go solo on normal difficulty.
Isn't that why when you get boosted, the booster clears the entrance to
the rift so it's safe, then you sit just inside whilst they go crazy
killing stuff on T6 or higher on that rift level. Rinse and repeat for
each rift level. No risk unless the booster doesn't clear the entrance