ereb can kite, minion ereb! of course he need to get close to trigger it, but thats all. he half ways kites and it is very effective.
of course you cannot catch up a good reg alone, no matter if he has poisoned dagger or not. only stupid regs wait for you to catch up. a good reg with fury and mines you will never catch alone as ub or oak. and even as ereb it will be hard. it is not the poison dagger. it only makes it a bit easier.
the benefit of poison dagger is when they play as a team! at the same time playing as a team yourself is the conter.
you are viewing this to much from a 1on1 perspective. let reg take anklet and then build like you suggested: you won't be able to kill him neither, nor flee from him. it is an anoying combination, poison dagger + this build, but it is not overpowered or similar like you seem to think.
you cannot kill him? ok, than kill the others or play defensive not being killed yourself. team up and set traps. end of story.
you want to kill him? buy wyrmskin (i think that were the gloves slowing) and skill slowing abilities + speed. he cannot slow you all at the same time. sure he can shot you all, but the dagger will not proc on all, and he will die in seconds when focused, slowed and only one of your partners being affected by the dagger.
use the advantages your other demigods have, like ubs dmg, erebs flexability, etc. and set traps where you can use your advantages.
edit: most times you realize the reg has poison dagger during the first minute. you cuold wait that time selecting your favor.