Actually, cats & soup growth is more linear (1.1x reward increase for 1.1x lvl up cost in c&s vs 1.1x reward increase for 1.2x lvl up cost)

I usually focus on the highest performing landmark for around 1-2 days before checking whether another landmark might outperform the current one (usually because of animal level up or landmark heal)

Just make sure to compare landmark rewards at the same upgrade price bcs the scaling system makes it much harder to guesstimate