Why do people consider bacteria to be 1. representative of the first replicators on Earth 2. primitive or unevolved?
Unless one is a panspermia adherent (which only pushes the location of abiogenesis somewhere else but not the root mechanism), bacteria are far to developed to have been the original products of abiogenesis. That would require a creationist leap in illogic.
Second, of all the lifeforms on the planet, bacteria are the easiest to follow many thousands of generation of morphological and molecular evolution. It is startling how quickly one can observe the accumulation and fixation of adaptive mutations under different environmental stresses in bacteria for example
Cooper VS, Bennett AF, Lenski RE. Evolution of thermal dependence of growth rate of Escherichia coli populations during 20,000 generations in a constant environment.
Evolution Int J Org Evolution. 2001 May;55(5):889-96.
Given that within a few weeks one can observe tremendous change in the genetic composition of bacterial populations, why would anyone expect modern bacteria of any species to resemble in any way, bacteria from hundreds, thousands, millions or billions of years ago?