With 3 defenses/saves, you're still getting a weakness, though. Odds are you can't cover all 3 very well with point-buy.
With 6 saves, there's likely a "I Win" button on every PC and NPC/monster. It's too much.
The problem with only 3 defenses is that some classes, those who already need one or two of those stats for their own features, have a significant advantage over classes who must have high stats in abilities that don't apply to ST.
And as for "I win" button, it's not bad for me. You still need to figure out which button it is, you still need to have spells or attacks that hit that button, and you still need to roll a dice to see if they work. So they are not so much "win" buttons after all (especially if the game is not going to feature many save-or-die), as they are effects that make combat more dynamic and various.
Well, this could be indeed an argument against a lot of Int/Str/Cha saving throws. But I would still keep the Con/Dex/Wis saving throws instead of 3 "new" Ref/Fort/Wil defenses/saves for simplicities sake.
That would be already an improvement anyway. With bounded accuracy, ST bonuses must be kept low and most importantly they must not scale fast. 3ed ST bonus progressions are probably too fast for 5e bounded accuracy. Hence, it's already better not to have any ST bonus progression at all, in which case using an additional terminology (Fort/Will/Refl) is completely redundant. They could even drop the term "Saving Throws" because at the moment they are practically just ability checks, but in this case I think it's better to keep the term as a legacy to previous editions.
As long as the save DCs can't outstrip the save modifiers, this isn't that much of a problem.
Intelligence, however, should probably be watched and handled more carefully than in 3e. Under 3e's stat damaging system, any spell that damaged intelligence was probably too powerful for its level when you consider what the intelligence score means - intelligence according to PC standards. There's no reason to believe an animal's brain or mind is less durable than a human's so intelligence damage didn't make much sense compared to other stat damage - too many creatures rated low because they don't rise to the level of human intelligence without any indication they should be more vulnerable to becoming helpless. But if the spells that targeted an intelligence save were about misdirection, detail, and processing information to befuddle or otherwise obscure some other activities, then I think the intelligence save could be a fun addition to the game.
And strength, of course, works really well against physical restraints, so I don't see why we should avoid using it.
And charisma allows the personality to overcome or resist attempts to constrain it. Maybe enchantment should be resisted by charisma...
Very good points!
Int damage and Int saves are of course 2 separate things. Since we're talking about Int saves, if animals have low Int by default, that would mean that they would be easy to fool with Illusions and maze spells. I don't see any problem with that... maybe rats and rat-typed creatures can get a bonus vs maze spells
Int damage (and ability damage) is not part of 5e, and probably won't be. I used to like ability damage, but I don't think they are going to put it back into the game, so there won't be a problem with animals, but if there was, one way to avoid it would be to make sure that such spells can at most lower Int down to 1 ("animal-like") rather than to 0.
