for someone who really never experienced it?

It's bad in the sense that it's an almost certain down if the Legion wants to tunnel you.

With the tape Legion can focus down a survivor in Frenzy and there is very little counterplay because you can't loop him because pallets don't work, and it's also hard to juke him because he can just look down, end chase and follow your blood and your bleedout timer forces you to stop and mend before you can get enough distance during his stun.

The reason they changed the deep wounds was to prevent this kind of cheesy chase tactics, because Legion players weren't using his power as intended (stabfest on everyone) and instead tunneling the first stabbed survivor. With Mixtape it was very quick and easy to down the survivor.