I'm playing on the default (Adept) so I'm sure the enemies are easier. and yeah, it's a little boring to use just a small subset of the spells, but at the same time I feel like I would be gimping myself if I didn't. Earth spells seem to have the highest DPS in general, and I have +105% earth damage, so it's pretty nukey. One launch meteor does 1700 damage for me to all enemies in a line at level 17, for "just" 180 mana, and leafy whip does 530 with a .4 second cooldown. Enemies that have 50% resist still take more damage from my earth spells than from other elements.
Tempting to get a set of more element-neutral enchants so I can mix it up a little, but it just so happens that I enjoy the earth spells best anyway.
I do think it is worth experimenting a bit, with all of the different spells. I've been finding that some spells I initially deemed as useless, really, really are not. I'd thought Cleft Smoglet was worthless at first; a spell that I cant aim? Turns out though, it's useful as heck.... I use it OFTEN now, and it's great against certain types of targets regardless of what weakness they have.
Or Ball Lightning.... there's a reason why everyone uses that spell, haha.
And I consider Insect Orb one of the best spells in the game, period. Ice Cross is pretty close.
But yeah, it's not all that necessary to bother with complicated loadouts on the lower difficulties (frankly, on Adept, you could probably get away with JUST Ball Lightning most of the time). On the higher ones, it's a necessity to diversify.
......also I just think it's more fun. Ball Lightning is great and all, but I get tired of it after awhile if I use it too much. I end up using most of the projectiles fairly equally.
If I had to pick a favorite element type..... probably Water, actually. Ice Cross and Ice Burst are both very strong if used right.... Tidal Burst or whatever it's called is unique in being a slower-moving piercing shot; it has a variety of uses, as just firing fast shots all the time isnt always the best solution. And that ice rock is similar to Earth's rock throw, or whatever it's called. And Geyser is amazing.
I think though, that some elements need a little bit of a boost in some areas. Earth has too many "big" spells, for instance.... Water and Air dont seem to have any. Air specifically is the only element without a background-striking attack (except for, I think, Storm Fist, but.... that really doesnt count, it's not meant for actual attacking). Fire has spells that can be a little too tough to use properly. And Entropy can just be kinda funky to use (but still very powerful). There does indeed seem to be a little bit of a lack of balance between elements as a whole.