Bitcoin is slow as hell. So you can do an order of magnitude more with Ethereum than Bitcoin.
So no, you can't "do" more, only be more noisy.
> Technically, decentralized system will be
> always slower than centralized one.
There are application where speed matters. For example, to sort things out while all the lawyers are in a room.
>bitcoin is significantly slower than other systems of its class
that class being decentralised proof-of-work, it is no slower than it is more secure than those class-members. (And among class members of equal 'speed' it is most secure)
Not inspiring confidence in the statement that it is faster than other systems. Compared to Bitcoin it is off by a constant factor, and constant factors aren't really what we're interested in here.
Storing an economy in a fully replicated global ledger has its limitations, there's no getting around that.