I wouldn't say it's the hardest game I've ever encountered. But say for example those stages where all the blocks fall down the stage, if you play as anyone but Alucard and use bat form to ascend, how is one supposed to beat stages like this? I guess ideally without a walkthrough you'd need trial and error for all of the levels.
That's Block 7-05 on Alucard's Cave Path.
Whether you get there via 6-01A's Catacombs or 6-01B's Sunken City of Poltergeists, you will HAVE to pass this on this path to proceed.
You just gotta memorize the blocks' pattern, which changes halfway through the stage (when the Mountains in the background are right at the center of the screen).
If you have Alucard and you picked up enough Hearts before the 2nd Giant Bat Battle (a Miniboss in 7-04A), you can actually fly to the exit, as mentioned, but you can make it with Trevor Alone or with Grant by just being patient and knowing the spots to jump to as the thing gets built.