I'm currently a lvl 35 Geomancer, so I'm by no means an expert in the field of Geomancy.
This is more my take on looking at Geomancer and voicing a bit of frustration at Square-Enix design process.
I'm going to get Geo up to 49 at least. I haven't tried subbing it to another job, but my understanding so far is: no Handbell = no Geocolure spells. What I don't currently know is whether subbed Handbell skill adds to Indicolure potency. If it doesn't, then this is a horrible subjob! (and that becomes gripe number 1: subjob viability isn't balanced, but that's not a gripe exclusive to Geomancer)
It seems like Colure spells are designed to be sparse. You should only ever have one out. The basic problem with this is, if Colures are unique, why are their bonuses so linear? It's like they are trying to make Geomancer just like Bard and Corsair, but with more graphical, resource, and effect restrictions (at least I assume Colure spells are graphic intensive on the whole).
It's like Square-Enix said, "We have a lot of levels to cover, let's stick in 30 incredibly narrowly defined buffs and debuffs so that players think they have a lot of nifty toys, even though they can only use 2 at a time!"
When I'm reading these forums, I see players asking for the ability to put more Geo effects out at the same time. It makes sense. I understand this desire. The sad part is that the design premise of Geomancer looks like it wasn't executed at a fundamental level.
There should be less Geomancy spells in general, but their effects should encompass more. This would validate a 2 Geomancy effect restriction.
Geomancer doesn't need a spell to enhance ally Evasion and another spell to reduce Enemy Evasion. It needs one spell that does both. It doesn't need a spell to Slow the enemy and another to give the party Haste. It needs one for both. Geomancy should DO more THINGS, not just ADD more NUMBERS in a spreadsheet simulator.
And that's what really gets me about the 76+ design process on the whole.
It doesn't make any job better, it just makes the numbers bigger and the amount of niche abilities go up. If you increase the number on niche abilities, don't be surprised when players gripe they need to be able to have more active at a time. The number of Spells in the Spell book don't matter if the number of spells you can cast is capped.