Thomas ... I helped run a Crappie.com tourney series for about 5yrs. We set the limit at 10/boat ... and we cleaned & cooked those & any "leftover" fish at the fish fry on the following day. You were allowed to catch & bring in up to a limit per individual team member, but only allowed to "weigh in" your best 10. The "leftover" fish, those that were caught but couldn't be weighed in, were thrown in with the weighed fish, afterwards, at the discretion of the team members. They could keep them, or release them, of course ... but, everyone elected to add them to the weighed in fish, for the fish fry. In the twice a year tournaments (Spring/Fall) over the 5yr span ... never was there a lack of fish to feed the participants & guests, regardless of whether there were only 5 teams or 20 teams participating. And, actually, we always had fish left uneaten ... which were usually divided up & given out to anyone that wanted them.
IMHO .... 10 fish per 2 angler team is a good "max". It might also depend on what's to be done with the fish, after the weigh in. If they are to be released, then the number could be lowered, as this would allow a better opportunity for survival of those fish, if they're not crowded & stressed over the course of the day. With most tournament rules stating that you cannot weigh in dead fish, and many anglers not having the best containment facilities in their boats, the lower number of allowable fish would help insure a better survival rate. And, like you say, "everyone can only weigh in the same amount" ... so, whatever number is suitable to the situation, would be appropriate. That might depend on what lake the tournament was held on, or what was to be done with the fish afterwards.
I certainly see no need to allow a full limit per angler, or even per team, even if that limit is as low as 15 fish/person/day ... as is the case at some lakes. The idea of the tournament is to catch the heaviest weight per allowable numbers of fish, in order to win whatever "prize" is being offered. The lower numbers of weighable fish still accomplish that feat, while not putting any undo stress on the population of the given body of water being fished.
... cp