My first thought – without knowing your background - is that the jump from PPL to multi IR is a huge one (e.g. C152 to Seneca), so you may well end up needing additional hours (and money) to bring you up to IRT standard.
On the other hand, there is a more gradual progression from PPL to CPL / multi to IR, as you’re going from a simple single engine type to a complex single, then multi, then the IRT.
Horses for courses.