I remember back in version 4.something I could usualyl planet hop through 2-3 planets without much problems with transports.
Nowadays it feels I'm lucky to get through one.
I can't really pinpoint what all has changed since back then (and I might be playing on slightly higher diff), but I've found that I can't really shatter my empire if I still want to be able to travel unless I make sure to neuter all planets on my back and forth route and keep their ship counts down.
Heh, this issue came to mind crystal clear yesterday when I started a new game and next to my home world was a mark IV world of Spireling diff 8 AI... A single transport could not even get my bombers to the command station although there were less than 100 mark IV ships around.
Overall that brief exposure to the Spireling AI felt like it should be made a 'hard' AI, it has over-ship-cap of many spire ships even on a world that has less than 100 ships. 10% of all it's ships being blade spawners... ugh, can you say ouch? With gravity drains all around you can't even get to them=)
Oh, two issues in one post, well, for the discussion feel free to ignore the latter, and focus on comments no transports=)