Agreed, though the aggregate combat potential of all starfleet ships feels a tad off to me, since we really do not have C0 ships, so I think some sort of Science to firepower ratio would be better to convey the goals of Starfleet...
Having said that, we also should keep in mind that the cap should grow as the federation grows and might grow if our neighbors start saber rattling or if we end up in a shooting war with a peer or near peer power.
Still, as others mentioned, the cap is soft, we can pass it (not that the council will be happy about that or that they won't be happy about it) still I am quite sure that in the scenario of us nearing the cap, we will probably see some restrictions from the council, like budgetary reductions or a request for us to either scrap or mothball older ships and, speaking of older ships, we might very well need to start phasing them out due to age or age related issues (either to the breakers or to the mothball yards and I am very sure the latter would take an operational cost to be run)
Hell, we could see ships getting an operational cost in BR and SR/year (after N years of operation or what not to symbolize the cost of keeping older gear working and could even start climbing till they become cost ineffective)