Stellar is a not Turing complete. Theoretically, it means it less powerful than the Ethereum smart contracts. However, theoretical computational power is just one measure of the power of the blockchain smart contracts. One has to consider whether major use cases require that power, and the ease at which these uses cases can be expressed in the programming language of the blockchain.
If one considers major financial and commercial applications, such as paying for goods and services, tokenization and security tokens, a common pattern emerges. All these applications require an atomic swap operation, where one and more quantities of digital assets are transferred between two and more parties, which has to be done atomically.
By atomically we mean, either all operations are executed or all fail. So we are talking on atomic transactions with multiple operations in a similar way to the execution of database transactions in the relational database world (SQL).
This fundamental atomic operation or as it sometimes called batch mode of execution is essential to the financial and commercial world.
Stellar with its transactions consisting of multiple operations offers this capability and hence major use cases can be directly and easily programmed in Stellar. In this respect, Stellar handles the major use cases much better than Ethereum.
In Ethereum, an atomic swap requires depositing multiple assets in a contract, using separate operations. Then, in a second phase, these assets are available for withdrawal by the parties to the transaction. Obviously reasoning on such contracts and testing them is much more complicated.
Even a simple two-way exchange of value between Ether or tokens and some material goods requires a whole escrow contract.
So while Stellar that does not have smart contracts with variables might seem with its operations to be of a lower level, offers the atomic transaction and atomic swap as a basic operation.
The atomic (batch) execution is so fundamental in the financial, and the commercial world makes Stellar more powerful than Ethereum in a major practical sense.