Why don't you factor in the possibility of more transactions per block? The idea is that as the Bitcoin transaction volume climbs, the need for a block reward decreases.
Secondly, you're assuming that the mining pool is currently constrained by what is profitable. From what I have read about large mining operations, they are significantly into the green on profit margin right now, so there seems to be room for a decrease in profitability without losing significant portions of the mining network. Every time the mining difficulty changes this is tested already so we know that there is at least some wiggle room in the mining profit margins.
You mean that the number of transactions grows faster than the mining capacity? I've covered a similar case in https://news.ycombinator.com/item?id=7846564 (it's #2). In general, if you want more transactions you also need a better security, which leads to increased mining costs.
That does not seem like a similar case to me. You specifically say "less miners" in #2. Plus what do you mean by mining capacity? If you mean actual GH/s then that's not a meaningful measurement because better hardware in the future will give higher mining efficiency at the same mining cost.
It just seems like you're oversimplifying a really complex equation with lost of potential outcomes. Perhaps this short comment style just isn't allowing you to explain everything. Have you written a blog or anything that details your thoughts on this?
Secondly, you're assuming that the mining pool is currently constrained by what is profitable. From what I have read about large mining operations, they are significantly into the green on profit margin right now, so there seems to be room for a decrease in profitability without losing significant portions of the mining network. Every time the mining difficulty changes this is tested already so we know that there is at least some wiggle room in the mining profit margins.