So, I believe you're thinking about this in the classic sense of security, transactions, and decentralizations. It's actually better to think of Ethereum as an ATM that replaces bank tellers - i.e. a fundamental technology shift.
Forget about decentralization/transactions for a second and let's take an example of your company transitioning your 401k to another plan. Think of all the people moving this money, all the legal process that it has to go through, all the find print that must be followed, etc. There's a TON of work to move a 401k and the process typically takes months. What if I told you that you could transfer your 401k plan, without the additional overhead of people, and you could do it in seconds? That's Ethereum.
Let's take another example of buying a house. If you've ever gone through this process it takes months to finish, theres tons of middlemen (bank loan process, approval, selling the loan, lawyers to secure the property, real estate agents, etc). What if I told you that you could buy a house, without this overhead, in seconds? That's Ethereum.
The bottom line is our current financial system is based on an army of lawyers, middlemen, banks etc. and large transactions take time and money to solve. With a concept like Ethereum you just don't need any of that, you can transfer large amounts of value instantly and you don't need this army of people.
It is frankly the difference between horses and cars. It's a technological shift that makes previously impossible actions possible.