For complex recipe graphs beyond vanilla train routing is also way more efficient. You get to reuse the same rail network, and sometimes not have to route dedicated belts for 6 low throuput ingredients from all over the map
I feel like a lot of the challenge in early Pyanodons is place-and-route and belt congestion. Unlocking trains feels amazing. They're definitely optimal for a lot of recipes in that mod I think
I haven't played the space expansion, but from old vanilla I only used trains for bringing ores to the main base. For rare low throughout recipies the flying bots (I forget the name for them) worked well, and towards the end of the game they got pretty fast as well.
As a longtime fan of trains in games like OpenTTD, it always felt like there wasn't enough of a focus on trains. Arguably this is something that Satisfactory did slightly better, there was more reason to use them there (that game certainly has other weaknesses though, and overall I prefer Factorio).