No, you don’t have to take Top-Up training every 3 years to renew your DS licence.
You ‘should’ renew your First Aid every 3 years, but at present (and for the foreseeable future), the SIA don’t have a checking mechanism in place so if you decide not to renew your First Aid, it will be kind of like driving your car without insurance, e.g you can drive a car without insurance, it’s illegal but nobody will know unless you are checked or have an accident.
You ‘should’ also ensure you keep yourself up-to-date on physical intervention in case you find yourself in court. You can do this by simply ensuring you visit the aid-memoir of the PI skills and knowledge you were provided with by your training provider when you took your Top-Up and ensure you attend any PI refresher training you are provided with by your employer. BUT this is NOT an SIA requirement.
The SIA review every 5 years and due to the changes this time around, I can’t (in my opinion) envisage any extra additional (mandatory) Top-Up training until (at least), circa 2030.