Prober, that makes sense.
When I go flying at work, I try to execute things under my control by SOP. Amongst other things that means taking off with the correct thrust and flap settings from the right place on the runway (and the right runway).
It also means rotating at the right rate from the right speed; I have to say that due to the vagaries of trim, different airframes and environmental conditions there is a certain spread to my efforts and those of my partner-in-crime on the day.
As to the effects? Well, Boeing FCTMs carry interesting diagrams showing slow and under rotation and the difference to 35’, which can be quite noticeable. Both errors cause the the takeoff flight path to be lower, which is undesirable and to be avoided (just to be clear) but not necessarily much more dangerous than normal in the way you might expect just by looking at it from the side.
If the power setting was correct, then stopping from <V1 should be assured. In the event of a thrust loss at V1, the general technique is a slower rotation to a lower pitch attitude - as the acceleration is less from that point there is more time to get it right, plus there might be a little more concentration from all parties.
Past V1 without a failure, in energy terms you are rising above the OEI flightpath with every second that you have AEO. Should you experience a thrust loss when airborne, you will be at V2+ and most likely getting a better climb gradient.
TL;DR: An improper (slow) rotation reduces margins but unless it’s so slow you don’t leave the ground, it’s unlikely to cause an issue, even with a subsequent engine failure. However, you should always aim to follow FCTM guidance as closely as possible (has to be said).