It is true that security might be weaker than the standard Discrete Log Problem. Basically the security reduces to what is known as the One-more Discrete Log Problem (a discussion of these types of assumptions can be found here https://eprint.iacr.org/2007/442.pdf). Which is probably a stronger assumption (meaning that it is probably easier to solve than the “normal” discrete log problem). However that does not necessarily mean it is easy. It is a commonly used assumption in cryptographic work and generally trusted to be secure, although a pure Discrete Log assumption is of course preferred.