Pep will have a plan and won't be buying for the sake of buying.
Mahrez could be see as an option on the left as well (also upfront). Just because he predominately plays on the right for Leicester, doesn't mean that will be the case with us. Sane played on the right at Schalke, Sterling on the left under Pellegrini (and might of done at Liverpool as well - can't recall). There's flexibility with different coaches.
Pep's earned the right to do what he deems fit. If he thinks that he can keep all these forwards happy, that we have to trust he can.