Probably for the best to see how Eleki does in OU. It's fast, but that's really all it has. No boosting move, needs to tera for coverage, paper bulk, mid offense, ect. I'm kinda shocked at the vote ratio tbh
It is worth considering that Regieleki's Speed is so absurdly high naturally (Max Neutral speed ties Positive Scarfchomp and Positive outspeeds Booster-d Valiant) that depending on your benchmarks, it can elect for an Offensive nature and EV into its bulk for certain benchmarks if need-be. The ability to run Rash/Modest alone makes it a lot more powerful than that Base 100 would suggest (closer to Base 115 Neutrals) on top of an ability that's "Adaptability but it works with Tera" (relevant since it wants Tera for Coverage)
(Mew chosen for a basic statline, this is to illustrate Power rather than the ideal move to click in Crunch vs IC)
252+ SpA Transistor Regieleki Thunderbolt vs. 0 HP / 0 SpD Mew: 202-238 (59.2 - 69.7%) -- guaranteed 2HKO
252 Atk Sword of Ruin Chien-Pao Icicle Crash vs. 0 HP / 0 Def Mew: 175-207 (51.3 - 60.7%) -- guaranteed 2HKO
Regieleki's Electric attacks pack a significant punch coming off a mon that
uninvested outspeeds Max Positive Dragapult, so Tera's Coverage for being able to touch grounds (not even OHKO itself, but just to prevent free-turns after chip as it did last Gen) is all it really needs in another slot. Eleki doesn't need to even commit to your Tera unless your Opponent still has their sturdy Resist/Immunity intact, when several of these Pokemon are heavily burdened Glues like GT, Ting-Lu, and Lando-T, or potentially passive Momentum sinks like Clodsire and Amoongus.
If there's one thing the game has been making apparent to me since Gen 6, it's that a low Base Stat is easily compensated by abilities and other boosts being piled on the Pokemon: Greninja's Protean coverage, Dragapult's ridiculously spammable Shadow Ball, or just funny calcs like this I saw as a joke
252 Atk Altaria Brave Bird vs. 0 HP / 0 Def Mew: 132-156 (38.7 - 45.7%) -- guaranteed 3HKO
252 Atk Salamence Dual Wingbeat (2 hits) vs. 0 HP / 0 Def Mew: 134-162 (39.2 - 47.5%) -- approx. 3HKO
Eleki is in the same boat, previously held back by its strongest moves having an omnipresent immunity that, while not gone totally, is much easier for it to circumvent now.