The blocking problem happens to the Skellies too, when they block the merc at choke points. As long as the mages don't get killed off so easily in the rear and on the flanks with the skellies holding the frontline, they would have served their purpose as support fire and extended sensors and light source of sorts.
As for Nightfish choosing to max Dim Vision in favour of Mages, he has good reasons but I have some concerns: as good as DV is, there is probably no need to max it. Against champions and bosses for whom DV is useless, Decrepify is probably the safest fall-back to buy some precious seconds of thinking and observation time before overwriting it with something else (probably only amp anyway). Another issue is the generous range of DV with +skills, at level 30 it might aggro more monsters than what is desirable, and we all know how crazy the monster density can get in hell...
With prebuffed mages and infinity, they can do over 10000 average damage. I still think that's pretty good. But if you don't have infinity or enigma, you should maybe put the points elsewhere. And even in single player hrs can't be that hard to get. Do hell countess runs and cube the dropped runes
I don't think you really understand how hard it is to get a high rune in sp, it would take approximately 14k countess runs to get 1 ber, 2 bers would take 28k runs. Or at 30 seconds a run 116 hours of countess running ....
Yes there are other ways of obtaining high runes (lower kurust running etc.) but is it really worth doing this to obtain an Infinity for a build that doesn't need it?
Well, I've taken the build through hardcore naked (naked character, not naked player) thus I don't really think mages are needed for safety.
Of course you can dump spare skill points in there, but I much prefer to max golem mastery and have a beefy IK Maul Iron Golem, which isn't really needed either but actually contributes to kill speed a little, especially against act bosses, due to crushing blow.
No comment @ runes are easy to get... XD Let's just say that while there are ways to get runes quickly I choose not to take those. What you do in your game is your own buisness but I am basing my guides on what can be done reasonably without resorting to hacks and cheats.
Yup, they are not needed. But I find them helpful in the sense that they are less sturdy than the skeletons and serve an extra indicator of safety. Instead of going on red alert only when the skellies get dwindled from 9 to 4, I know it's time to pull back a little when I'm left with less than 2 mages.
Mages help with kill speed too when they don't get killed, as I recently proved against hell baal