The answer is yes. Glaser for example will include a F18 measurement form with their sails, they are certified class measurers on the F18 side and I would fully trust them to provide accurate sail area data to compute a SCHRS rating. Any of the lofts building A-Cat sails should also be capable of the same.
One issue with the SCHRS rating scheme is the mainsail area includes the mast. So you need to measure the mast area. That is pretty straightforward. It helps to look at the F18 measurement certificate which clearly outlines how to measure sails and the mast. The US F18 class website also has detailed photographs of sail measurement. Its about 1 hr for a 3 sail boat.
I hear you, but applying DPN corrections to SCHRS doesn't work. We've played this game locally. Get your sail area if that is the change and run the calculator. It is easy because the numbers for almost every boat are readily available online, type those into the excel calculator and update the sail area. I do this for our fleet, maybe you can designate someone for your local fleet?
Unfortunately SCHRS doesn't differentiate between pinhead or square top sails etc. They do have a sinking correction factor which I think you should use for the Isotope, and on the 2018 rating calculator this gives you a SCHRS number of 1.072, quite a bit slower than a 1 up F16 (1.041). Without this I get a number of 1.057, again relatively slower than a 1 up F16. I used a board depth below waterline of 0.56 m, the number for the Taipan 4.9 (which in stock configuration has very short and stubby boards). You didn't post a number from what I can tell, so that may be part of your ratings issue. Personally I feel the 1.057 number is a fair rating considering the following statement on the Isotope website:
"The Isotope Catamaran is a registered Formula 16 boat!
The hulls meet the 16ft LOA requirements of the Formula 16HP class. The strong points of the Isotope are that its balanced helm allows it to out point any other catamaran to windward. An Isotope meeting the One Design class specifications can be raced as a single handed Formula 16 boat. An Isotope with a spinnaker can be raced with crew in the Formula 16 one up class."
If the hull doesn't plane, maybe the 1.072 number is fair, maybe. How does the boat sail compared against a 1 up Blade, Falcon, Viper or Nacra F16?