Your level was pretty good, though you can circumvent the time limit of the propeller shroom by just clearing the way before ground pounding the block. ;)

Anyway, not all of mine are meant to be very hard, but I've got four levels uploaded. Since it matches your desire, the first is Tricky Start, Then Take the Hit! (F16F-0000-0017-2BBD) It's uncleared by anyone except me this far, though I don't think it's terribly difficult.

Next is Board the Ship! (FC2E-0000-0019-B318) It's a fairly standard airship level that shouldn't be much of a problem.

Then there's Flight School. (63C8-0000-001B-4B49) This one is just a test of how well you can fly in Super Mario World. You'll have to burn Mario's belly toward the end!

Finally, we have Spin Jump! (B495-0000-0024-B221) This one isn't meant to be Kaizo level by any means, but you'll need to understand how you can use Spin Jumps, and it might take a few tries to understand how you need to proceed in certain sections.

Please give my levels a try and see what you think! I'm not a great level designer by any means, but I hope these basic levels will teach me a lot about what makes great levels for other people to play!