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When Weaver lost his velocity in 2012 his Ks went down and his XBHs went up. His ERA was excellent in 2012, but his skillset declined from 'ace' to 'TOR'. Then since 2013 he has gradually declined each year.
The drop from 94 to 92 wasn't significant for Felix as it was offset by him becoming a better pitcher. The drop from 92 to 90 will be much more significant as his skillset is close to maxed out. It will harm the effectiveness of all his offspeed pitches.