I agree that the dadworthiness of a man should influence the decision about whether to marry him, in the twenty first century. Families now are very different from families then. We have modern psychology telling us that the father's involvement in the care & rearing of children is very important in the formation of their characters. But Regency England--how involved were Dads there?

Mr. Bennett spends all his time in his library; Sir William seems more involved with being a Sir than helping with homework.
As a father, Mr. Collins might be expected to be like his own father--miserly (at least not illiterate), he would probably be very concerned that his children be extraordinarily well behaved around Lady C., but I surmise that their rearing would occupy him very little & that it would be all Charlotte's doing & that she would do a great job.
Genetically, we are not given to understand that he is that deficient & that JA seems to ascribe his oddities to his upbringing. After all, he & Lizzy & Jane are from the same gene pool.