Not sure why you think the data from the miner to the pool is irrelevant, I think it requires more computational resources than the former, and the block template/work sent by the pool is nearly identical to all miners (with some pre-determined minor changes), the submitted shares need to be checked individually and thus probably require a lot more resources.

So while the "traffic size" from the pool to the miner is larger, the "computation power" is higher for the return route, correct me if am wrong.

With that said, we are talking about a few hundred bytes exchanged every "MERKLE_REFRESH_INTERVAL" which is probably 30/60 seconds for most pools, any decent pool should be able to handle hundreds of thousands of miners regardless of their hashrate, I am not aware of any mining pool that requires a minimum hashrate, they all have minimum difficulty and that's all about it, you can mine with a Pentium 1 CPU if you wish, it's all just matter of getting any valid hashes or not.

On a side but related note, posting consecutive posts is against the form rules and might get your posts deleted if someone reports them or a mod sees them, please edit the first post to include the other 2 replies and delete those.

Good luck.