Like, in terms of actual boosts to your SPM, Vulcanus gives foundries (a bit over 2.25x iron/copper production), Fulgora gives EM plants (bit over 1.5x circuits, which is better than it sounds as it is multiplicative with itself), but... Gleba gives biolabs, which are an over 2x bonus to SPM *for free*, *and* you get prod 3s which are a +8% prod bonus to all electric furnaces, +12% to chem plants, +16% to assemblers, and a net +28% to your labs (resulting in a total of x2.56 science from those, ignoring quality), which very much adds up over time. And you get a bit over x1.5 to rocket fuel, heavy->light cracking, and light->petroleum cracking, if you're willing to import bioflux which you need to do anyway for biter eggs.
(Edit, because I realized this wasn't stated: Vulcanus and to a lesser extent Fulgora's buildings require you to make a way bigger base to actually use all the increased resources you get. To use all the iron and copper foundries give requires a correspondingly bigger everything-else. EM plants only help with circuits, everything else is going to have to scale up to match them. But for Gleba's bonuses? You just rebuild labs and maybe your science builds to use a few more assemblers/a beacon or two to deal with prod 3s reducing machine speed more than prod 2s do, and if you want to, your oil processing to use the better cracking/rocket fuel recipes.)
Sure big mining drills give x2 to ore patches but Gleba lets you get literally free iron/copper/carbon/sulfur/ice/calcite from space with the advanced crushing recipes, meaning you don't even need to mine ore patches (you can easily send lots of ore down from space now in 2.1 with the new unloading bays so that part isn't an issue)
Sure Fulgora gives the recycler for quality upcycling but Gleba gives epic quality in the first place. (Okay admittedly you need both, but.. you can gamble a few epic equipment pieces with just Gleba.)
Sure you get artillery on Vulcanus and sure Fulgora gives mech armour but Gleba gives spidertrons which do the job of both, and lets you have effectively a remote player on every planet.
Sure you get green belts on Vulcanus for x1.33 throughput on belts but you get stack inserters on Gleba which give you x4 throughput for a lower cost.
The only things I really miss from not doing Fulgora and Vulcanus earlier are cliff explosives, the recycler, bot speed research, and a foundry on Fulgora for holmium plates.
(And no Gleba is not that hard if you just make sure to put a spoilage outserter on everything and circuit limit your agri towers to not put too much fruit on the belt. Bots make it trivial if you just set up a spoilage requester somewhere, set all requesters to "trash unrequested", limit all outputs to one stack, and make sure things are close... maybe direct insert a few things like yumako mash/jelly. And the pentapods are a non issue as soon as you get spidertrons researched. I find it easier than Fulgora to build a 120SPM base on, and you have no risk of anything running out of raw materials as everything is literally infinite, not even just figuratively infinite like on Vulcanus, except stone.)
(Also if the devs see this, pretty please make the biochamber actually useful on all four planets like the other main planetary buildings, maybe make it able to make holmium solution?)