Seriously? Playing 7 "right" (I.e. not getting hit, low level and finishing battles in under 2 minutes) requires a great deal more planning, timing and on-your-feet thinking than anything in 13...
Dude, really?
Bit of a false equivalency I think. You can of course come up with whatever set of arbitrary challenges you like to skew the balance of anything. But 7 and 13 were just designed with a different basic challenge curve, and trying to finish 13's regular battles in an amount of time comparable to random battles from other FFs really isn't the same thing as a challenge run.
To comfortably get through all the non optional content in 7 except demon wall and maybe Seph, with minimal challenge and frustration, you can just use a basic mix of attacks, summons, and LBs on pretty much everything (obviously Weapons not included), no fancy strategy, no precise timing required. You can put extra work into thinking up cool Materia combos that will overpower you, but even without doing so most people I've talked to who played it (who are certainly not power gamers) saw very few game overs, and didn't find the game challenging (of course this isn't to say some may not have found it challenging, just haven't encountered many of them).
It's true that rav/com/med will get you through a chunk of 13, but it will lead to time out losses against plenty of bosses, and will result in incredibly drawn out and frustrating regular battles, particularly in the back half of the game. Which is likely why many folks I know who tried it hit a wall and quit on a boss they couldn't beat. To make the game feel comfortable, you pretty much HAVE to use more advanced strategies (atb refresh, careful management of buffs and debuffs, unusual paradigms like tri-sentinel or tri-rav). Note, I think this is a design flaw, because minimal planning and heavy use of auto-battle will get you through a good chunk of the game (though as others have noted this becomes far less viable after reaching pulse, a difficulty spike not mirrored anywhere in 7). So, many people take the easy (and boring, seriously, some of those battles go on forever) route, stick with med/rav/com and maybe rav/rav/com, and then find, not surprisingly, that the battles are boring, drawn out, and, at first, mindlessly easy.
See I think 13 was designed at first to be challenging, but they worried people wouldn't put in the effort, so they rebalanced it around time - playing the battle system the way it genuinely feels to have been designed rewards you with faster more engaging battles. But it's not sign posted, and it's not really necessary for much if the game. I think this because most random battles in the back half of the game require 6+ minutes with auto-battle and basic strategy, and no sane person would design random battles that take this long. Play them carefully, and many can be cut to a minute or less. Which is much more in line with the basic approach random battle length in the rest of the series.
7 is still fun to play without a ton of planning/thought. Random battles are fast and snappy, and much of the enjoyment in battle is from spectacle (summons, LBs). And, of course, there are the very challenging side battles that require combat mastery (which honestly is almost entirely Materia combo tactics). None of this is true of 13.
So, all in all. I really do think 7s battle system is better tuned.
But 13s is a lot harder. Many bosses require unconventional tactics, and normal encounters do too if you don't want them to drag on forever. If you put in the effort, 13's system is more engaging and rewarding than 7s. And again I say this as someone who prefers 7.
This is also true of Lightning Returns, but is not true of 13-2, which sacrificed the tactical depth of the first game in response to lots of complaints about difficulty in 13.
Edit: much more economically, what he said ^
