i dont know what kind of casters you're running into, but mine typically out kills the entire party (even one with 3-4 casters)...it usually looks something like;
me: 64
rest of party: 10
on the average gianthold quest...
i don't use metamagics (other than heighten) and i'm definitely not a damage build...i blow through anythings sr (i think i've got a +22 with maxed enhancements, 34 cha and spell pen feats) and the dc on my worst spell hits a measly 29
firewall still crits at over 120, average tick is somewhere around 30-40 points on a regular mod
i've yet to meet a tank that can keep up, considering i can easily solo most quests without recalling for sp provided there's at least one shrine
now, i do have two tanks (one capped, one 13) tricked out with every weapon you can imagine (dual weilding vorpals, greater everything bane, smiters, paralyzers, banishers, disruptors, cursespewing, you name it i've got 3-4+ of them) and am lucky to get a dozen kills with a caster equivalent to mine in the party (unless it's a quest like gh tor where things can't be instakilled)...i can out kill dps casters (to some extent, average 1h swing is 35-40 on a non-crit, but with critting on a 15 for 2x-3x hitting an 80 average isn't hard) but no way can i touch a caster where everythings dead before it gets within view, this makes for a very boring tanking experience (oh yay i get to loot a chest and break down a door here and there...and i get to fight the end boss)
nerfing metamagics to take down dps casters will result in dc/FoD/Pk casters running rampant...sure two max/empowered dbfs can take down your average mob for a few hundred sp, but you've gotta use the same sp cost to take out 1 guy as you do 20...
i say leave it the way it is and fix the AI...dancing around in a firewall without being under the influence of something (like say, dance sphere) is just stupid...and being able to take out a whole mob with fod/pk before they see you is as well, i think the major issue here is the AI, not the players...there's always going to be uber builds and someones always going to find something that's overpowered, thats just how it is with MMOs