There should never be a challenge level limit because lvl 50 players can have completly unleveled cards and a lvl 2 player can have completly leveled cards, there for that throws the lvl limit out the window, the other thing is that the random generator that dictacts you wins and losses seems to take into account lvl there for giving lower level players a slight atvantage not taking into account skill and technique. o and lower level players get a massive amount of XP if the beat a higher level player.
IT's a give and take situation. You can't limit by level because of the rasons Bill gave. Joining a guild is a good idea since depending onthe guild it will have training, access to hard to get cards, and strategies.
Another good approach would be to play EVO for a while to level your cards up.