Seat tube dents from Front Derailleur band-on. Is this gonna get worse over time?

Hard to say what will happen, but it does look like an aggressively tightened bandon strap front derailleur. Unusual that it had enough clamping force to distort a frame tube - must have been phenomenally tight and fitted by a gorilla.

I think the best thing to do is keep an eye on it, and if things change or get worse, then stop riding and re-evaluate.

If the bike is brand new, it may be worth a warranty claim. If you've had it a while, then that is unlikely to fly.

The other possibility is that these frames have a pre-crimped mark to help wiht assembly of the front mech - can you look at another one to see if they all have the same mark? I've seen similar on some models, with clearance dents on chainstays etc.

It's fine, no issue at all on a 4130 bike. Could have been caused by putting an FD on a weird diameter tube that was close to but not quite 28.6. It's safe to ignore.