i think there are two issues being mixed up here.
first of all, at the moment platforms are automatically assigned by the route finding logic. that is a flaw that is known by the developers. which is why they are definately going to introduce waypoints either for the release version or shortly afterwards, depending on their workload of fixing major bugs and such. thus we will be able do define which platforms are going to be used by lines so that they are evenly distributed and 6 lines won’t pile up at one platform.
secondly, it will most likely not happen that trains might choose an alternative platform if their designated platform is blocked by another train. i guess whether you see this as a drawback or not might be dependend on where you are from, because i believe that in the UK it is common for train dispatchers to assign platforms on the fly, while in germany and switzerland, trains always stop at the same predefined platforms. over here trains will only go to different platforms if there is a major disruption that necessitates it. and the handling of disruptions is obiously something that goes much further than is the scope of this game.
so if we are looking at passenger trains in train fever, a blocked platform might occasionally stop a train from entering a station, but only for a very short while. which is even realistic because real trains occasionally need to stop in front of a station as well. and regarding freight trains, if trains pile up because they need to wait for a full load then there are too much trains on the line for the production capacity and even if they would choose a different platform, it would not improve anything because it is the goods production that is the limting factor, not the stations capacity. so trains will pile up anyway and if there were multiple lines transporting multiple goods at this station then you would even disrupt your other lines as well. so in this case, use the waypoints to make your trains wait outside the station, which would again be quite realistic.