Pentamelds used to give you more total primary stats because you could overmeld primary stats, allowing you to trade in secondary stats for primary ones. If I understood the live letter correctly, while you will be able to fill existing slots in the new gear with primary stats (i.e. your guaranteed melds), you will only be able to overmeld with secondary stats. If the new raid/token gear is meldable, that could make up for the discrepancy, but you'd only be able to compensate with one strength materia per accessory - the four overmelds would need to be secondary stats.