The IOTA Tangle solves the scalability problem. If it works as advertised, Tangle would add a lot of value to the IOTA (MIOTA). For example, Tangle could serve as the basis of cryptocurrency credit or debit cards or a blockchain banking platform.
The Tangle might give IOTA a much higher level of security than existing sidechains. The problem with sidechains is that they have a lot less encryption than blockchains.
The Tangle would offer more security and capacity because it is larger and more complex than existing Sidechains or blockchains. The complexity alone generates more security.