Good points, thanks. I was kind of basing/weighing this on the brawlers card "Parting Blow" (cost of two, limit of two). As far as the moving one square at a time: I don't think it's that critical when the interrupt is declared(?) Sure, your 2 points/2 cards limit is similar but Partying Blow has 2 key changes:
1) Parting Blow Stuns the figure playing it which is a huge difference especially for a melee character like most Brawlers. It means unless you're Bossk or have some other way to remove Stun you probably won't get an attack + move the next round. Your version doesn't have any downside like this.
2) Parting Blow requires a very specific trigger of a figure moving away from your brawler, which probably happens only once in an activation and only if the Brawler moves adjacent usually. Your card is written such that it could be triggered anywhere in a very wide area so the threat range is huge. Even if you know your opponent has it in hand it would be very difficult to play around. This is a big part of why the trigger matters.
So you've taken Parting Blow, removed 2 downsides, and made it work with a wider range of figures. That's why it would be overpowered.
At the very least it should probably be worded the same as Jyn's ability that only happens when a figure starts an activation within LoS of the Overwatcher.