Remove pathology until it's balanced.

[GORE]

It should be noted that, AFAIK, symptoms available to be put into a pathogen are randomly generated each round. Naturally as a result one is not guaranteed to be able to make a beneficial pathogen...

I think you mis-understand how the symptom randomization.
There's a large block of commented code in 
GitHub\goonstation\code\modules\medical\pathology\pathogen_dna.dm
that explains it, and I'll summarize.

The more T1 symptoms there are, the more they game can have of each other tier. Every T1 gets a 3-char DNA sequence at random. T2 is made from taking every T1 DNA, and prepending and appending it with T1 DNA. We have 8 T1 symptoms so far, allowing for 56 T2 symptoms (8 permute 2). So long as the code has fewer than 56 T2 symptoms, it assigns each symptom one of the 56 generated sequences. We have 11 T2 symptoms currently.
Generating T3 is similar. Take each assigned T2 DNA sequence, and add T1 DNA seq (before and or after) to make as many sequences as possible. Then assign a random sequence to a T3 symptom. The math gets harder at this point, because I spared some details about collisions, but I'm fairly certain we don't have enough symptoms to worry about locked symptoms.

Counts, because it was part of my research:
T1: 8
T2: 11
T3: 10
T4: 12
T5: 11

We have 8 T1 symptons but was there not a recent change that there are only 6 base-pairs left? Leaving us with 6 of 8 T1 symptons each round.