Having had numerous jobs is not likely to be a red flag. Should NOT be any reason for concern just because a person changed jobs frequently.
BUT the following is NOT correct:
. . . obviously employment history IS A FACTOR in the decision-making. It is such an important factor that leaving a gap in employment history is enough for IRCC to return an application as incomplete. While that alone is a significant decision, it also illustrates how important IRCC considers this information in its processing a citizenship application.
What role employment history has in the decision-making is a big subject in itself, BUT for the vast majority of applicants there is NO reason to think twice about it, let alone worry about it. A complete and accurate work history is NOT going to cause problems.
The gist of it is about how all the individual parts fit into the whole picture, comparing details, such as comparing work history, address history, and travel history, looking for anything that signals incongruities or inconsistencies that raise questions. But for sure, the applicant's work or school history is an important part of what IRCC evaluates in its assessment of the applicant, and the applicant's actual presence in Canada in particular.