Take away Tau marker lights is certainly going to help you the most, and i agree that Eldar are squishy and slow once they get out of their transports, Wave Serpants are tough nuts to crack at AV12, jink, cover saves, serpant shields, turning pens into glances, etc, etc
Grav weapons will be helpful for most MCs wounding on a 2 or 3+ but even though Space Marines are the only ones who get the fancy new grav weapons IMO your best bet for dealing with a high toughness MC is still Sternguard and Hellfire rounds