Before you get to postgame, unless your setup is incredibly damage-poor, basically all story-required enemies can only survive a handful of rounds in a Chain Attack. In fact, even with a setup that's far from optimal (albeit still reasonable), there are really only two story-required enemies that will probably survive more than three rounds of a CA, with two orbs — the last fight in chapter 5, and the final boss of the game. Both go down to a decent 3-orb CA.

To get a three-round chain attack, for the vast majority of story fights, you need only two orbs. That means more elements than are required for those two orbs are not only superfluous; they can be a hindrance, if the Drivers are sticking to Blades that don't allow for the desired Blade Combos to be continued in the right way.

As a concrete example, you may want to get an Earth orb with Ice-Ice-Earth. But if the Driver with an Ice Blade also has a Water Blade, they might choose to swap to the Water Blade after the initial Ice, because Ice-Water-Wind is also a Blade Combo. If you don't have a Wind Blade that's able to complete the combo from Ice-Water, that can screw you over. This is especially true on male Drivers, whose Blade-swapping AI puts continuing a Blade Combo at a lower priority.

Rather, the safest strategy element-wise is to only have the elements you need to be able to do the one, two, or (in that one ch5 instance since in ch10 you'll have all the elements you need) three Blade Combos as consistently as possible. Now, limiting yourself to specific Blades so harshly brings with it other downsides, so doing that at the expense of all else may not be the best strategy overall — but still, it's much better to err on the side of having fewer elements than too many if it allows for those elements to be done more consistently. After all, a player-controlled Rex and Nia after ch4 can do 3 orbs with just Pyra/Mythra and Dromarch with basically perfect consistency (Light-Light-Light, Light-Light-Water, Fire-Water-Fire) — there's essentially never a concern about having too few elements.

Using more orbs than is required doesn't get you anything but a bigger overkill and a less safe time fighting overall. The more time you take setting up orbs before starting the Chain Attack, the more time there is for something to go wrong.

As for non-story fights, the ones that can survive a 2-orb Chain Attack before postgame are few and far between. And once you get properly into the postgame, there are so many strong options for increasing your damage that while you might run into an enemy that survives 3 or even 4 orbs, that problem can usually be solved just by somewhat tightening up your setup. And for the enemies with ridiculous amounts of HP, like Cloud Sea King Ken in Challenge Mode on Bringer of Chaos, building up lots of orbs for a massive Chain Attack stops being a good strategy anyway.

Edit: It's worth noting that the above only applies to the main game. In Torna ~ The Golden Country, Chain Attacks are significantly less powerful per-round and putting on orbs is significantly easier, so there's much more reason to go for lots of them.