There are plenty of 1000 ton plus ocean going patrol craft about.
There are a lot of ocean going vessels well under 1000 tons. The US Army has a fleet under 800 tons. If coastal patrol craft are included why not include armed Boston whalers and ridged inflatables? I served on an ocean tugboat with a Boston whaler work boat - and we used it in the ocean. The LCUs I sailed on spent a lot of time on open ocean runs. I even ran a Mike 8 between Japan and Okinawa, a few times during typhoons.
Yeah what Im saying is that there are “patrol craft” around that are fairly significant surface combatants of today. I mean, there were destroyers in WWII that were no bigger (and quite a few even smaller).
These things are very hard to accurately describe because there is probably less of a consensus internationally as to what constitutes a “frigate”, “destroyer”, “corvette” or whatever now than there probably ever has been before. I personally would describe a patrol craft as a moderately fast sea-going gun armed (only) warship, probably with some kind of helicopter carrying (or at least refueling) capacity.