I was a little worried about this until I saw the the AI running around with the sensor ships I designed. Now I figure all is fair. Also, those sensor ships are super fragile and cost you 1/2 your initial credits, so its not like it is a choice without risk or opportunity cost.
This is another good point. If the AI can take advantage of this as well, then it becomes "equally broken". And one of the things that Lead Designer Paul Boyer has said on occasion is that he doesn't mind if thigs are 'broken' if everyone can take advantage of them equally.
If the AI isn't crippled by this, then what's the real concern?
As for this is an "obvious" choice, I personally disagree. Maybe it's because I run on large(r) maps, but I tend to rush a couple of proto-survey ships my first few turns. They have more move, life support, and, yes, scanning capabilities than what I already have. But they are designed to explore my immediate area and then be turned into full fledged survey ships once I get Interstellar Survey (which is almost always within my first ten techs or so). Then I crank out a few Cargo Survey Ships among my Colony Ships and whatever else I am building at the time. Not so much for revealing of the map, which is nice, but to suck up all of the anomalies I can find. I find the bennies I get from the "goody huts" FAR outperform whatever advantage I might get from building a pure Sensor Boat right away.
In fact, I tend to wait till turn 70 or 80 now before making sensor boats, since my Cargo Survey Ships are are already doing the mapping job for me AND getting those precious precious anomalies before anyone else. Really if anything in this game needs nerfing, it's anomalies .
Maybe I'd do it differently on a Tiny or Small map. But on Medium and above, you'd better believe I am building my actual fleet of exploration ships before I build ONE pure "sensor boat".
In fact, I build order goes something like this:
(Proto) Survey Ships/Colony ships
Constructors/Initial Military ships (if needed)
Constructors, constructors, and more constructors
Then and only then do I start to think about sending out any "Survey boats". And that's usually so I know what is going on in "my" space before I even use them to see what's going on elsewhere.