Some common sense tidbits about those Panspermia ideas
Ratio of 'Age of Universe' to 'Age of the Earth' = about 3.
Not a million-billion. Just '3'.
The numerical equivalent of a penny. Hardly worth walking over to pick it up off the floor.
Chemistry 101 Rule of Thumb: Chemistry slows down by about half for each 10°C drop. Space is generally cold. Cold might be an advantage for certain delicate molecules, but most often it just slows things down.
Warm puddles are generally faster. Much faster than frozen asteroids.
So, those proposing any of these sorts of Panspermia ideas need to clearly explain why cold space is significantly more conducive to making these life precursors than all the endless variety of environments found on the nascent Earth. Next multiply the (dis)advantage of cold space by the likelihood of the necessary proto goo then traveling through space and reaching the Earth. Finally consider the total quantity landed on the sterile Earth, and the resultant odds of it being put to use. The net final answer is that this Panspermia idea is either more, or less, likely than the canonical 'warm puddle' on a nascent Earth.
Until they address the above point, it's all just useless noise.
The answer appears clear, but maybe there's some subtle advantage to ultracold chemistry that needs to be explained. I remain open minded, but highly skeptical.