Does a bad paper get rejected very fast and if a paper is under review for long time, should one expect at least reasonable review?
No.  There are tremendous differences across journals.  A "bad" paper can get rejected within hours after submission, or 6 months after submission.  Good papers can also get rejected within the same timeframe.  Some reviewers are very conscientious and complete the reviews quickly, but the paper can still sit with the editor for a long time.  Or, more often than not, you have multiple reviewers on much different time schedules.  Some journals do a very good job of triaging papers, so a rejection of a bad paper may happen quickly.  But you will learn that "bad" is a very subjective viewpoint.  I suggest that you do not associate the quality of the paper (i.e., good vs. bad) with the time under review.