Only Yagudo was not soloable, and only because of a door you had to get through. The other two and everything else in Yagudo was soloable if you prepared for it and paced yourself. If you expected to get run in and get what you needed, you died very quickly. Even with the true sight mobs (Orc/Yagudo) at the end, if you waited patiently for them to turn their backs, they wouldnt aggro. The True sight Quadav was the same, but you just waited for him to move away from the ???.
I will note that the difficult to solo was also dependent on whether the HNM was up or not, though it was rarely the case.
---------- Post added 2013-06-19 at 02:31 AM ----------
I played FFXI hardcore from US launch till sometime in 2006 and then off and on since and also consider myself an altoholic. FFXI was also a one character, all jobs game and I loved that aspect and welcome it in FFXIV. As to whether or not everyone will be as unique, I'd say yeah. My Tarutaru was pretty unique on Fairy, even if customization was every limited in FFXI (only 8 models with 2 hair variations each). And even if you level up all jobs, people still tend to favor or are better with a certain job over others. Yeah, it does make it easier to forfill a role if you need say, a healer, but it no different then jumping on an alt you had leveled to do the same.
As for altoholics, it takes a different meaning. Where a lot of people I know in WoW (including myself) or other one character class, one job MMO will level an alt for a different class, In FFXI or FFXIV, you dont have to. However, if you want to play through some lore, you can start a new character for the other cities. There are three starter cities with unique story line through lvl 15 and later starting at lvl 20, you can choice one of three Grand companies to continue your storyline with. So if you wanted to see all aspect of the lore, you have to make a alt (at least 2 others) and start in a different city.
Hope that answered your questions