Oh yes you’re right it would
But if a blockchain becomes very large then the probability that at some time over the years there will be a Internet outage covering a large area will cause all copies of one chunk to be inaccessible is not insignificant. The outage could be political or technical and may last from seconds to a much longer time. And you could be in the small segment and have lost access to most files on SAFE till the outage is over.
So while the network will recover when the outage is over the blockchain is deemed broken and useless for mining or node use during that time.
This I believe is a major consideration when someone decides to use SAFE to store a working node or mining.
NOW the other more important thing for working nodes and miners is that it involves a lot of databse access across the blockchain. For a working node this is looking up balances and transactions for reporting to a user or payment system. For a miner it is for validating transactions and solving them. The miner has to ensure the address has enough BTC for he transaction so has to do a database lookup on every address in the block being solved.
The time for access requires index then block lookups for each search. This could be as little as a few chunks to hundreds of chunks for each address balance/transaction lookup.
When on your local disk its quick real quick – milliseconds. But from SAFE it could be seconds.
So storing a blockchain on SAFE for the user who is running his own full node wallet then its great, but for a working node or a miner then it will be too slow in my opinion.