***MINOR SPOILERS(FOR SOM)***
My main problem with SOM was similar to your VI end game issue, I always viewed the dyrad spells on both chars as pretty useless, so the game dumps a final battle that the only magic level that really matters(besides perhaps the cure spell) on both your mages was the dryad spell(plus I was used to nuking things with my mage
. I'm pretty sure my first game, they were both at level 1 or 0, and the spell lasts pretty much no time at that level. Its beatable(esp if you have gotten any of the special armors in the final area), but still annoying.
***END SPOILERS***
On VI you have a point, but I think its pretty common for people to find at least the moggle charm, and with just that you can reduce the requirement to 8 chars or so(and with the amount of force char usage here and there, hopefully you have at least 6 reasonablly developed, prob more so if you don't know what chars its going to force upon you at certain points, I find it gets easier and easier to not have enough developed chars when you know whats going to happen--of course being forced to use x, y and z when you haven't used them much yet might force a bit of grindyness whenever it happens, but should at least spread it out some).
For IV, yeah the moon is the first time it gets tough. Part of my speedrun involved knowing what to run from (starting about there the list goes way up--many things just really aren't worth killing at that point)--Still have to grind a bit for the final boss though so he doesn't 1 shot the weaker chars too much. I'll have to do another of those over christmas break or something, its been a while.
I picked up the DS version recently, and you have to grind at least a little even for the 2nd fiend(the water guy), unless you want to replay the battle until you make 0 mistakes(basically timing your spells right) and get lucky that he doesn't silence someone when you need them. I haven't had the time to grind past that part yet.
At this point I've played both of them way too many times to make reasonable assumptions on what a new player plays like though (plus with stuff like gamefaqs, I really wonder how many people honestly play through their first playthrough blind these days).
At the risk of going off topic on an off-topic post:
If you are interested in pretty much non-grindy but high difficulty, theres a romhack of final fantasy tactics that fits the bill(ff v1.3--partially due to the fact that enemies pick up power at a faster rate than you if you try to grind
. I'd suggest playing through the original first if you havn't though, since it starts out pretty hard, and only gets worse(and seems to expect you to know the basics). Oh hey, I haven't checked it out in a while, seems like theres an easytype version out now(that includes alot of the balance changes, but not quite so much difficulty).