I keep seeing this "without a save" as if that's the context here. You have to HIT. Spells are EITHER you have to hit OR you have to save. There is no meaningful difference really - either the player rolls a d20 and compares it to a target fixed number (AC), or a Foe rolls a d20 and compares it to a target fixed number (DC). So there is just as easy a way to avoid this attack as pretty much any other bog standard spell or attack.
You have to hit. That's essentially the same as a save or an opposed check. It's still all just a d20 vs a target number, with the foe setting the target number with their AC.
And if this somehow freaks you out, literally every single PC and foe can do the same thing without a cantrip at all. They can just grapple and shove! Or grapple and move you!
Why is moving someone seen as overpowered somehow, after five years of this stuff and literally nobody ever saying anything like "wow forced movement is breaking my game" here, or the WOTC before they shut down, or on Reddit, or on FB, or anywhere?
And why, when I asked for actual examples from real games where this did something meaningfully "overpowered" am I still getting theoretical responses? I think that's not a coincidence. I don't think it's all that powerful, and people are fretting over nothing. If I am wrong in that assumption, there should be a slew of people posting about it, for years now, because it's soooo common. levitate, dissonant whispers, telekinesis, Bigby's hand, thunderwave, etc.. there is just so much that forces foes to move. Why, all of a sudden, would this one be broken because it uses AC for the target fixed number instead of a fixed DC (or opposed roll)?
Well, that's an incredible amount of snark and attitude. Thanks for that I guess.
I have seen variations on this discussion/thread before on multiple boards from GitP, to RPG.Stackexchange, to here in earlier threads, so there are people out there talking about it.
No other unlimited use ability in 5e can push an opponent away from you from up to 120' away or also force them to move up to 40' and has no limits on the size of the opponent you can move.
A Pixie Warlock could Eldritch Blast a Great Wyrm Red Dragon back 40'
Personally, no moving someone 10' on the board isn't breaking my game. I would have zero issues with it, if it were limited to 10' once per round like Grasp of Hadar, Lance of Lethargy, Thorn Whip, Lightning Lure, etc.
It's the unlimited, incremental scaling nature of the Repelling Blast that raises my ire. Especially in multiclassing scenarios which have broken games I've been in before (SorLock I'm mostly looking at you).
It is such a good ability that almost every Warlock I've ever played with takes it whether they are focused on EB as their thing or not. That tells me that it's a bit over the top.
Every other ability in the game requires you to be much closer to your foe, from in their square (grapple) to 60' away (Levitate) and usually costs you something other than your action. Levitate and non-cantrips cost you a spell slot and are also much closer range than EB can be. Cantrips besides EB with Repelling Blast are limited to 10' once per turn. So are EB's other rider Invocations for that matter.
The physical options, grapple and shove, are limited to one size category larger than you. To grapple or shove someone is an opposed check rather than just a straight to hit or save. and you sacrifice your damage to do so.
At my table it forces me to design encounters around Repelling Blast for every battle. I have not yet found a battle where Repelling Blast doesn't change the nature of the encounter all by itself and at zero resource cost to the party.
I can't have battles in open space with single opponents (Huge or not, flying or not) or the warlock can solo them by keeping at 80-110' away and just pushing the enemy back constantly. No one else even has to raise a weapon with that ability and it cost the Warlock none of their resources to do it.
I know that 5e punishes single monster combat, but without Repelling Blast in the repertoire, at least there is combat, not just kiting.
It forces me to swarm or have large #'s so that other people have something to do or only have indoor battles or invisible foes or fight at range, or some combination of all those, or... etc. It very much limits what I feel I can do as a DM to make a meaningful and fun combat encounter when Repelling Blast is at my table.
The fact that I have to to take it into consideration with every battle design, means that it is too good at its job.
If it were just 10' once per turn, again, zero issues from me. But it's not.