I have searched online and there is little information about the disadvantage of a circular DNA. Since I know that with chromosome arrangement like human, we have telomere that held the DNA strands together, which loosens as the organism ages and the cell divides. With circular DNA there is no need for telomere and the number of times for the cell to divide is greatly increased. Then comes my question, does circular DNA has major disadvantages? And if a multicellular organism has circular DNA arrangement, does it have a longer lifetime?
Per se, there is no disadvantage of one type of DNA over the other. They evolved for different reasons, and the fact that both are still present indicates that they fulfill their role(s) satisfactorily. There is no competition between the two types of DNA. Even multicellular organisms (eukaryotes) have circular DNA within their mitochondria, and both genomes cooperate for a proper functioning cell (and there's even gene transfer from the mitochondria to the nuclear DNA, and there is also translocation of mitochondria). Most multicellular organisms have chromosomes instead of circular DNA, although there are some multicellular bacteria with circular DNA, so these would not 'suffer' from the shortening of the chromosome ends, but take into account that aging is due to many factors (oxidation, protein degradation, membrane degradation, etc), so it is not the sole responsability of telomeres to extend the lifespan of an organism.