There does not seem to be correlation between the length of the genome and the size of the animal, just as with the number of chromosomes. Most bacteria have 5 - 30 million basepairs, but as you note the amoeba is a notable exception. Amoeba proteus at 300 billion isn't the largest, the organism with the longest genome is amoeba dubia with almost 800 billion basepairs. Virus genomes are measured in the thousands. Also, there are species of bat and deer with 50% - 70% of the length of most mammals. So the relationship between the size of the genome and the animal is unclear. Note I am not a biologist.
That is all I wanted to point out.