Fixed that for you. That Prague has 47 development. This player conquered a total of 134 development (more than half the starting total development of England) from Bohemia with local nobility and Czech ideas, without bothering to counter it with admin ideas. I don't see a problem here. If you
really want to annex this beast, take admin, influence, and plutocratic ideas; vassalize Bohemia and activate the two policies that reduce diplo-annexation cost.
It's also worth noting that Prague starts with 21 development, which means Bohemia must have spent far more than 940 MP developing it. I'd call this fair.
edit: I got curious, so I checked with Wolfram Alpha to determine just how much it would cost to develop Prague from 21 development to 47 (assuming no events helped to boost it, which to be fair is highly unlikely, so this will be an upper-limit). Plugging in
sum((50+5n)(1.06+.01n), n=0 to 25), the result I got was 3539.25 monarch points (with both economic ideas and a university in Prague, it would be
(.66+.01n) for 2369.25); natrually, the game itself rounds off with each successive development, but that's way more math than I'm interested in doing. The true cost will be within 26 points of that number.
This strikes me as a perfect example of the advantages of tall play: mash development, get local nobility, become too troublesome to conquer; the one problem with this is of course that for a deterrent to work, your enemy must be smart enough to appreciate the threat.