The new 7.3L is certified under the using the EPA's Dyno certification. These numbers report lower than the former Chassis-certification numbers.
When Ford was required to do the Dyno certification in the F-SuperDuty Chasis Cab, the V10 became rated at 288 HP, and motorhome became 320 HP. Although some programming changed at this time as well, to reduce emissions under the new greenhouse gas standard for medium-duty trucks.
Here is the PDF describing the testing differences:
https://media-cf.assets-cdk.com/teams/repository/47d/f3c08de6a1005810f0050568ba825/1/SuperDutyChassisCertificationVSDynoCertification.pdfWhile the 6.7L diesel does have mechanical differences between light-medium and true MDT applications, Ford has published in a separate document that 7.3L gas engine is mechanically the same, and has the same programming whether chassis or dyo certified.
So, this is an improvement in raw HP over the current 320 HP V10.
The 365HP V10 was only chassis certified. This number should be compared to the 7.3L's chassis certification, where it's rated for 430 horsepower.
https://media.ford.com/content/fordmedia/fna/us/en/news/2019/08/01/ford-73-liter-V8-best-in-class-gas-power-torque-heavy-duty-pickup.html