Thats a poor mekor, that is talking about rabbonim and it is talking about a country which is run by botei din, this doesn’t apply nowadays.
The short answer is that both are needed, yes, learning Torah has tremendous benefits, but we also need a standing army to physically defend our land, yaakov did this when he heard that Esav was approaching him, why can’t we?
And anyway a year and a half under the hesder system is a small contribution and hakaras hatov to the country which allows us to learn freely when you consider that you will have the rest of your lives to learn freely and you can learn a bit (not much but a bit) in the army itself