Light currently has a pretty solid pool available, with the addition of light Tsukuyomi. Not the best (cause water's the one that has it all), but solid.

The first goal/ideal to strive for is to try hit as close as you can to a total of -50% with your atk and def debuffs.
For atk, light can hit -50% through Sol/Raphael (or Belobog)/Sniper Shot. Or, you can hit 45% if you replace Sniper Shot with Outrage from Mordred. Sol's -20% C-frame atk debuff is <i>really, really</i> good.
For def, light hits 50% through light Tsukuyomi/Diana/Sniper Shot. Or 40% if you replace Sniper Shot with Outrage.

Thunder would be an example of an element that's currently weak in this regard; needing future kamihime for more debuffs. I think that Tyr and Raiko are literally the only current thunder kamihime with debuffs. So pure thunder currently peaks at -35% atk/def with Sniper Shot.
Fire's in a less bad state, but current pool is still behind Light. Amaterasu or Konohana Sakuya provides -20% B-frame, while Enma provides -15% B-frame. You can get -15% A-frame atk from Raguel. -10% A-frame atk from Baphomet and def from Nergal (both R's and available from gem gacha, so everybody will have these two). With either Amaterasu or Konohana Sakuya, you can hit 40% in one of atk or def (via -20% A-frame atk from Joan or -20% A-frame def from Gawain), then 30% or 35% in the other. Right now, you'd probably opt for -35% atk/-40% def.

After debuffs should come other utility.
Sol's got healing/debuff removal/buff removal. Sol's a freaking good utility piece.
Raphael offers overdrive orb removal. Nice thing to have.
Belobog's got debuff removal too. Situational, but nice to have available from an SR. A regen too for supplementary healing.
Overall, Light's doing fine here too.

I think that Light being weak would be a carryover from maybe pre-Diana. Definitely pre-light Tsukuyomi. Right now, Thunder's behind because of a dearth of things that aren't punching someone in the face. Fire's behind from still needing some more help with debuffs as well as having a bunch of SSRs that are considered weak enough to either receive buffs in half a year, receive awakenings eventually, or both.