Moving from 7.4 -> 8.2 will be just as much refactoring as moving from 7.4->8.0->8.1->8.2. Security support is in general three years [0] so everything 7.X is now unsupported. Considering the security cadence you can skip one version, but if you skip two you'll probably be out of security support before you migrate to a new version. My philosophy is if you're going to need to do the work to upgrade anyway, you might as well do smaller chunks more frequently and be able to take advantage of the language goodies that come out earlier.
The amount of the language that gets deprecated every year is PHP's fundamental flaw, at least in the last five years.
GP's problem seems to be that they have to support WordPress plugins and themes that they either can't or don't want to patch by themselves. This is a different situation from people who build & maintain in-house apps. In that case, always using the previous Ubuntu LTS is a perfectly viable solution. Stay 2-3 years behind the edge, giving enough time for the plugins and themes to get updated, while still receiving security patches and comfortably within the recommended range for WordPress Core.