I am not a geologist or an expert in any of these fields. However, the canyon at Mt St Helen's was formed in hours. The flood lasted a year... I do know how fast water can erode rock and I also know the power of a mud slurry with various sizes and types of rocks and it's ability to grind and pulverize autogenously.
The destruction of a few hours, compared to a year is note worthy.
I have been to Joggins. The tour guide makes it quite clear of the age of each layer of strata... Yet, the trees go right up through these.
The roots are on the trees, not because they were growing... but because they were yanked from their places and frozen in settled mud and rock in a very short period of time.
Like I said, I'm not an expert... I do firmly believe that, in the end, all will be revealed and God's Word will be shown to be the solid truth.
Saying that you aren't an expert, of course doesn't justify your ideas. You seem to be aware of the shortcomings of your claims. You should seek justification for them, rather than just blindly throwing the claim out there, in hopes that people would just blindly accept them.
If you're unsure of how fast rock can be eroded by water, just Google it.
People have pondered the same question before, many times.
Biblical Creation vs Evolution- the age of the Earth
And no matter how you crunch the numbers, there is no research supporting erosion of rock at any rate in which 5,000-10,000 feet could be eroded in a single year. The only exception is in cases of mass wasting, which is not the case of the Grand canyon.
Mt St Helens (the aftermath of the eruption) is an event of mass wasting, combined with loose and unconsolidated rock. It is the best of both worlds with respect to high erosional rates, whereas the Grand canyon would be the worst of both worlds with dense rock, great depths and features such as meanders which display a low energy means of erosion (the opposite of mass wasting).
The Grand canyon is really the opposite of Mt St Helens, geologically.
And with that I'll move on. The same goes for your suggestions on polystrate fossils. You should justify your ideas rather than just blindly throwing them out on the table.