Spore Druid and Call Lightning is absolutely amazing. A level 3+ spell that you can cast infinite times without expanding further spell slots? Oh hell yes, please!
They need to think more creatively. You're now focused on countering the enemy caster, and the party might be more distracted helping you to clear out the threat.
This is the perfect opportunity to take advantage of, and put some nice pressure down.
Nah, the group where I play the caster who could take Counterspell has a fairly green DM and I just don't want to stress him out more by thwarting his plans.
With a veteran DM? Boy I am fucking them every which way front, back and sideways with creatively misused utility spells.
A player having access to counterspell is need-to-know DM information just like a player having access to flight is. It can and should be planned around.
Also, if the player and DM are into it, escalate the arms race, start having enemies prepare counterspells. Lots of interesting casters have it on their lists but DMs are afraid to use it to its full potential. Players would do it to enemies all day long but when the tables are turned, nobody ever forgets what it's like to have the enemy lich counterspell their heal.