People will quite happily secure their online banking or whatever with a 10-12 character password... if you use UPPERCASE + lowercase + numbers... that's 26+26+10 = 62 possible characters... then we can throw in the 33 ASCII printable "symbol" characters like ~!@#$%^&*()_+ etc... and all up it would be 62+33 = 95 characters in your "fixed and known list".
So, a 12 character password using this list would be: 95 * 95 * 95 * 95 * 95 * 95 * 95 * 95 * 95 * 95 * 95 * 95 = 540360087662636962890625 possibilities.
The 2048 word list that Electrum uses means that your "alphabet" has 2048 characters... so that means your 12 word seed is effectively a "12 character password where the alphabet has 2048 characters" in it. Giving up this many different seeds: 2048 * 2048 * 2048 * 2048 * 2048 * 2048 * 2048 * 2048 * 2048 * 2048 * 2048 * 2048 = 5444517870735015415413993718908291383296 possibilities...
vs
5444517870735015415413993718908291383296
If you're not worried about someone hacking your 12 character password, you don't need to be worried about someone hacking your 12 word seed.