What you were reading are rules for several different Electric Sailplane contest formats.
The contest that has the 1/2A motor rules is an LMR type of contests. LMR = Limited Motor Run. Its a totally different contest from ALES.
For ALES contests, there are NO motor rules at all. You can use what ever you want. Inrunner, outrunner, big or small, long or short doesnt matter.
Some clubs do have different classes within the ALES format, but they generally focus on the model in some way. Foamies vrs everything else or maybe 2 meter and smaller vrs open class or beginner vrs expert class.
I dont know of anyone who is doing any kind of motor limits in an ALES contest.
Now, with LMR type contests your question is very relevant. LMR contests reward the best motor performance you can get from that size motor. The goal is to get to altitude as fast as possible.
In an ALES contest you do NOT want excess power and you do NOT want to get to the altitude too fast. The perfect ALES launch gets you to 200 meters in exactly 30 seconds. No sooner and no later. if you get there sooner, you are giving up soaring time to your competitors. If you get there late - you are giving up altitude.
So its kind of like Goldilocks - you want your power system not too big and not too small. It needs to be just right
For ALES, that works out to 120-140 watts per pound.
That said, buying quality motors and esc's and batteries will give you lighter components for the same amount of power. So it pays to get good stuff if you want to be a serious player. Weight is your number two enemy with sailplanes. Drag is number one