Honestly, going easier on the climbs doesn’t really work that well on group ride like this if you want t do the fastest time possible.
It is worth it to go super deep on a climb if it will keep you in the group which you can roll with on all the flat between the climbs. Rather than going a bit easier on the first climb, voluntarily dropping yourself, and riding the next valley on your own or with a slower group.
Best case is you arrive at the bottom of the final climb a bit fresher and can go up it a bit faster, but you are still way behind were you would be, or worse, you go up it slower because you had to ride relatively harder across the flat.
Obviously the caveat is that if it a 20 minute climb and the group you are in is going so hard that you know you will only be able to hang on for minute then you should probably cut your losses, but if you think you could just about hold on, go for it.
You also have to remember that for pretty much every domestic road race, and sportive, the first hour is always flat out if you want to be in the front group, like unsustainably flat out because the strong guys want to get rid of the weaker guys. I have never done a road race were the last hour is faster or even the same speed as the first hour. If you want to be in the front group, you just kind of have to go all in and stick with it.