Growth tightness and genericity for word metrics from injective spaces

Mapping class groups are known to admit geometric (proper, cobounded) actions on injective spaces. Starting with such an action, and relying only on geometric arguments, we show that all finite generating sets resulting from taking large enough balls (as in the Svarc-Milnor lemma) in the respective injective space yield word metrics where pseudo-Anosov maps are exponentially generic. We also show that growth tightness holds true for the Cayley graphs corresponding to these finite generating sets, providing a positive answer to a question by Arzhantseva, Cashen and Tao, who asked if any of the mapping class group's Cayley graphs is growth tight. To achieve the above results, we consider the space of all geometric actions of a mapping class group, and for any injective metric space in this collection, we construct a sequence of word metrics that converges to it and show that all large enough terms of the converging sequence inherit many desirable properties from the limiting injective space.