Yeah, that’s valid, there are a few common layouts for SRE. I would call what you’re describing a horizontal layout (each team owns a layer for all apps that use that layer).
It sort of comes back to support levels. Your Infra SRE teams stay small if either a) an app SRE team owns application specific stuff, or b) SRE just doesn’t support application specific stuff. Eg if a particular query is slow but the DB is normal, who owns root causing that? Whoever does needs headcount, whether it’s app SRE, infra SRE or the devs.
It sort of comes back to support levels. Your Infra SRE teams stay small if either a) an app SRE team owns application specific stuff, or b) SRE just doesn’t support application specific stuff. Eg if a particular query is slow but the DB is normal, who owns root causing that? Whoever does needs headcount, whether it’s app SRE, infra SRE or the devs.