I have 20 jobs, they all need gear. I like the game, so I play them all and gear them all. I also have a ton of furniture, I like decorating my moghouse, I like gardening occasionally, even though in the 4 yeras I've played only one person has been in my moghouse, I still like to keep it looking fantastic.
When gearing 20 jobs, I have to make sacrifices, such as getting a universal gear thats a stat or two less then a job specific gear. this I dont mind, but my whm set alone is about 60 spaces of inventory. I know guys that carry over 80 items for one job alone, so saying stick to just a few jobs isnt cutting the mustard arguement wise. Especially since abyssea, things have changed, lots of people have 8-10 jobs leveled and geared now these days, I'd say 6 main jobs geared well is very common. And lets face it, a well geared job takes up 50-60+ or more spaces of inventory alone.
PS: real quick, consider this, before the trial of the magians, I carried 8 hq staves on blm alone, now, I carry more because you have you 30% macc hq staves and your mab affinity ones. Now, like I said I cut some corners because I have 20 jobs so I only have the 4 magian staves, and carrry on blm/rdm/sch another 6hq for various reasons. Just right there is 10 slots, and we haven't even geared ourselves yet. Most sch have all the elemental obi. My goodness, what if one of the 4-6 jobs you suggest I focus on is sch??? If I only had a few jobs as suggested, I would still need more space because I'd focus more on a few jobs and they would have more gear fot that job, not less gear over all.
Another prime example, right now, I currently always have in my mog sachel these items that most every serious player should have, it's not about inventory management, please, it's about loving the game and playing the game at your best:
echo drops
holy water
remedy
poison potion
instant warp scroll
instant reraise scroll
meat mithkabob
tavnazian taco
bream sushi
toolbag (shihel)
cream puff
marinara pizza
red curry bun
reraise earring
warp cudgel
Thats just the food/medicine I carry. One cant say being prepared is a bad idea, any vet would have to agree carrying this is the minimum. i carry the instant scrolls so I dont need to waste gil on the cudgel and the earring, but i carry the earring and the cudgel for when time is not on my side to replace the rare/ex items and I gotta be somewhere fast or forget to replace those items. Cheap foods and expensive foods, different medicines for various effects. I might join a shout that is leaving immediately, if i forget to bring items I'm screwed and so are the people depending on me. Reguardless if these items are in my moghouse or on my person I still need to have them somewhere. That's just a small list, my storage is completely filled with +1/2 and empyrean weapon item upgrades. last year, I had both my locker and my storage full with +1/2, since then, a year has passed and I've been able to convert most of these items into storable armor.
I do understand where you are coming from, I've had to rethink alot of gear that I held onto but really never used and have since tossed or sold them.
Also, what about if I want to level crafting while im camping a nm? Crafting alone requires enormous inventory space if your trying to stay in one place thats away for a major city for awhile.
How about procing on any /nin job in abyssea for magic proc? That's another 7 inventory spaces there, because the tools used cost 10-20k a stack, so after I purchase a stack of tools and only use 5-10 per run, if that, I'm left with something I cant sell back on the AH now, nor would it be effective to toss becasue of the cost and I'll just need them again eventually so I'll need to store those, too.
If my only two jobs where sch and thf/nin, from just the common items I mentioned above, without gearing them at all, that's 7 stacks of seperate tools to proc magic weakness, 6 elemental obi (I only have thunder I havent finished the others so I dont know off hand if there's a light and dark one but if there is I wont be doing them anyway so), 6 hq staves, 4 magain tiral staves, 15 misc items previuosly mentioned, for a grand total of 38 items. That's not the job specific or even making a mention of gear for those jobs, no furntiure, nothing but the staves for the sch and his/her obi, and dispossible items. I'd say that's alot of needed space being occupied and we havent even begun to talk about putting on gear, furniture, anything indepth.
Also, I carry all eight geode and 8 avatar named mineralites (such as titanite) and each of the four seals (beastman, kindred, etc). Why? Because if you want to collect them, you need space to stack them. After all, they are worth gil or crafting skill-ups, stack to 99, can be used in trials or for bcnms. That's another 20 spaces needed, and we still aren't talking furniture, gear, etc. Total space used so far, 58.