The problem is that even if the dynati are broken, any Emperor who switches attention away from the army is going to be inviting defeat and invasion. Whilst a frontier might be temporarily pacified, such peace would never be stable, and sooner or later a strong adversary would (re-)emerge. A raiding naval force could work, although even then I think it would be used as an adjunct to the army, rather than becoming the senior service in its own right.
The problem is that even if the dynati are broken, any Emperor who switches attention away from the army is going to be inviting defeat and invasion. Whilst a frontier might be temporarily pacified, such peace would never be stable, and sooner or later a strong adversary would (re-)emerge. A raiding naval force could work, although even then I think it would be used as an adjunct to the army, rather than becoming the senior service in its own right.
Possibly the only way I can think of (and I won't lie, this is a shameful way to tie in one of my own threads), is if you have a fortified border (such as S.Anatolia) as that allows the need for the army to be reduced.
It isn't in the timeframe suggested, but another way is with the rise of ocean-going trade. If we say our in-timeframe PoD is that the Empire expands, retaking Italy and Africa, you could have a Roman-Italian explorer discovering the New World, or surviving being blown off course trading with West Africa by sea (because bulk shipping salt and gold is cheaper).
So big Roman Empire that relies on ships to both maintain control of the Med, the Red Sea (and Eastern Trade Routes), and Atlantic Trade. All of which requires a large navy - that high-level of growth and the economic reliance on those trade routes should elevate the navy to prime importance. (Side note : I love the idea of a Morocco/North Africa that lives and breathes Atlantic Trade in the way that Spain did IOTL).
It isn't in the timeframe suggested, but another way is with the rise of ocean-going trade. If we say our in-timeframe PoD is that the Empire expands, retaking Italy and Africa, you could have a Roman-Italian explorer discovering the New World, or surviving being blown off course trading with West Africa by sea (because bulk shipping salt and gold is cheaper).
So big Roman Empire that relies on ships to both maintain control of the Med, the Red Sea (and Eastern Trade Routes), and Atlantic Trade. All of which requires a large navy - that high-level of growth and the economic reliance on those trade routes should elevate the navy to prime importance. (Side note : I love the idea of a Morocco/North Africa that lives and breathes Atlantic Trade in the way that Spain did IOTL).
That's more or less of what I'm getting at. Except that role would be seen as crucial and thus offer slightly more prestige then what the navy got in OTL.