HH, true to a point except our aim is defence and deterrence. Provided the kit we have today offers sufficient capability to deter then we don't need better kit today.
Where we need to use the kit, provided we have sufficient numbers of the right capability today then we don't need new kit until tomorrow.
I am not advocating no F35 just don't need it until we have a requirement, like equipping a carrier or replacing the GR4.