I'd argue that it's only too fast for aliens, but for my own ships I don't complain, it takes me long enough to explore, let alone find a decent system, anyways. Maybe it's because aliens grow exponentially while I don't because even if I have the capability there's only so much tasks the CPU in my head can handle at once.
How so... the game are not really an RTS...
I think you just build too few survey crafts if that is the case. At 100% survey exploration is extremely quick.
You should be able to multi-task as much as needed to expand as fast as your resources allow you to do.
I could've built more but I don't really need since exploration speed >>>>>>>> expansion and colonisation speed. And the game has so much mirco to do I can't focus on everything at all time, from chosing new worlds to terraform and colonise, setting permanent routes of citizen transport to support growing colonies, designing ships (and designing and researching 23468712346 components needed for this), flying ships and fighting, setting mineral routes, supplying colonies with installations, deciding what dto build, building and designing missiles... Holy smeg it's so much, the CPU in my head handles aurora similarly to the CPU of my laptop, it runs at 100% and can process only so much at a time.
When you get over the fact that 90% of the game is logistics you realise that you need to not get ahead of yourself and plan accordingly. That is why I usually emphasis that the game is about the journey and not the goal. When you pass that insight you can spend hours planning and setting this up carefully and then run the game slowly and adjust as things change and new information is gathered.
You need to have extensive notes outside of the game to remind you of logistical goals, planning colonies, income and production balance and all that. If you are not in such a hurry to reach the next technology or find out what is on the other side of the galaxy you should be able to keep up with expanding and doing all that is necessary.
You know what resources you have at your disposal, you know what resources you can acquire and so you can plan to expand and what you need to expand. In general I find if very bad to go after an NPR unless I have a decent tech advantage over them, which I rarely do as I start at conventional and give the NPR at least a 150-200% bonus head-start in addition to that. The more I need to focus on offensive military operation the less I can focus on expansion and industrialisation of my colonies.
The game have enough automation that you should be able to keep pace with expanding much faster than the NPR do once you get the momentum going. As long as you can secure your Corundium income you can expand as fast as you can allow your population to grow.