Considering that a wizard trying to get the Philosopher's Stone will probably be a powerful one, why didn't the professors put much more difficult obstacles in the Underground Chambers?
Is it because they already know that the obstacle made by Dumbledore is impossible for an evil wizard to solve?
Edit : To clarify :
The puzzles to enter the Ravenclaw Dormitory are not easier than the puzzle of Snape.
Quirell's mountain troll is probably the easiest one for a powerful dark wizard who does not care about using the killing curse.
McGonagall's chess puzzle is solved by a 11 year old non-professional chess player.
Flitwick's winged keys puzzle is solved by Harry Potter, who is an inexperienced Quidditch player who played Quidditch only for a year (if we don't count his babyhood).
Sprout's Devil's Snare can be solved by using many spells if you don't know that you need fire like Hermione did.
Hagrid's Fluffy can be solved without the precious information that you need music to put it to a sleep.