The timing is a little unfortunate. 5.6 will be too late to make it in for 20.04, but 5.5 isn't an LTS kernel and 20.04 is an LTS distribution, so I understand not wanting to use 5.5.
If you compare the flexible version targeted at June, and the non-flexible version targeted at August, you'll find that they're making almost the exact same compromises.
Nothing ever stops you from using an earlier version if it's more stable. So both schedules get to chose from multiple versions. Maybe flexible chooses from 6 month old to 3 months in the future code, via delaying. But non-flexible can choose from 9 month old to 0 month old code. It works out the same, and the only difference is how you label it.
The reality of doing LTS, plus LTS .1 mean that the next standard release didn't get as much attention. So in reality the first six month release was often very rough, with a lot of new things in it that would be straightened out over the course of the entire cycle.
As someone mentions later in the thread Canonical started doing HWE releases, which means you can run a later kernel on the LTS. So I'm running 18.04.4 (I think) which has a HWE kernel that is newer than the one that originally shipped - not just security fixes but newer hardware compatibility.