This may be a “your mileage may vary” situation. When I was trying to get a town of 750 people, it was barely growing and holding around 650 despite ample cargo supply and passenger train connections. I added a town transit service and bam! Another 100 population within a year.
But I rarely provide trams or buses mostly because, as you mentioned, it’s such a pain to regularly replace the vehicles all the time. I wish there was an automatic “replace/upgrade until I tell you not to” option associated with the route or road vehicle garage.