Agree with you, Frank, 10 images is over the top for my tastes, as well! I allow only 1 or 2 in my contests. Sometimes, if the subject/theme is not very popular, I will allow both paintings & photography. But, you're right, it's best to ask for one or the other.
My advice is don't enter the ones allowing 5 to 10 entries...or those allowing both types of work! Or, better yet, host your own so you can make the rules. But, you will be removing paintings from your 'Photography Only' contest & vice versa! Some members simply do not read or follow the rules.
Contests are mostly for fun & simple promotion, not to be taken too seriously. That being said, we hosts who do 'it' well appreciate a note of 'thanks' for our time & efforts...once in a while!