Besides this, more importantly, each hash (ie difficulty of 1) has the same probability of solving the block as 1/1024 of a miner hashing at difficulty of 1024 (accepted share with difficulty 1024)?
Only a difficulty share 39.5 Billion or higher will solve the block at this difficulty level. A diff 1 has no chance of solving a block as it doesn't meet or exceed the current difficulty, neither will a diff 1024.