What I don't really get is how fast the exo waves arrive after each other. We've had 3 waves in the last 1.5 half hours and another one is built up to 65% again. I find hardly any time to expand at all since most is spent on rebuilding my/our fleet.
The first few exos will be smaller and thus charge faster. The interval between them (and their size) should generally increase by about 25% each time unless the provocation for them is also increasing. Also, if by "Everything is on" you mean Spirecraft - Hard, Golems - Hard, AND Fallen Spire then... yea, you're going to be facing frequent exos for the rest of time
Though unless you've got your first Spire City already you're only currently getting exos from the Spirecraft and Golems sources.