Breakpoint for Minion gem levels?

I just bought a wand that gave me +27% dps.
My old one had+1 level to all minion skill gems, so i edit the new wand to see the impact and it only adds +0,7% dps.

So i wonder why the +1 wands/helmets are so expensive?
Is there a breakpoint to spawn more skelletons or what?

Yes, you don't get +1 skeleton for every level to the gem. For a list, check this wiki link https://www.poewiki.net/wiki/Summon_Skeletons

For raw dps, Skels, zombies, and golems all get around 11% more base damage per level, up to level 30. After that its about 1/2 as much.

Then i dont get it why i only gain 0.7% when i editet the +1 level to my wand.