So... paladin and rangers just have to lose all of their (fine, most since paladins get LoH) self healing ability here? Do they not qualify as melees? You can argue a ranger shouldn't tank even though they can and evasion is nice for a tank, but the DDO devs have solidly put paladins in the "tank" category. I really dislike the MMOification of DDO and the attempt to force everyone into the holy trinity because it is easy to design for. I do understand some of the need because this is an MMO, but it is one that is built on flexibility and customizability, don't take that away.
It might be better to think of Lolth as an encounter that discourages self healing through SP and other "regen" tanks. We have bosses that discourage hitpoint tanks by having effects you don't want to get hit with and non-evasion tanks by having lots of reflex spells, so having one discourage "SP" tanks isn't that far of a stretch.
If 250 seems too high, maybe the devs could lower the number to something like 50 and put a temporary stacking debuff to max sp of 200, discouraging you from getting hit several times if you have a sp bar and if your max drops below your current sp, you lose those too. I agree that 250 sounds large, but I have not personally played the raid yet.
I want to take Shade's word that it is easy to control aggro there, but he could easily mean you just simply engage your cosmic magneto-plasma hyperdrive to travel back in time to kick over Lolth's sand castle when she was a child thus insuring her wanting to attack you today. Not everyone has a CMPH, knows how to drive it through time, or where Lolth liked to vacation as a child. Easy for Shade does not mean easy for a lot of people, you are quite the player from what I've read. I fully expect many sp bars to be drained by this attack because nobody can swap aggro properly.