A jerk DM is gonna be a jerk DM whether you cast Conjure X or not. That isn't the fault of the Conjure X spell mechanics.
Alas a jerk player is going to be jerk player with summoning spells too and as a DM I have the right to prevent that from happening. I don't want to see 8 giant owls spammed and slow down play and prevent everyone else having fun so here is how it works at my table.
1. I have random tables of summonable monsters for each CR and the player may summon.
2. I also have removed the CR 1/4 option and have a single table for CR 1/4-1/2 which are run more like swarms than single monsters and summons 2 such creature swarms/packs, so you will be 2 packs of wolves rather than 4 individual wolves.
3. The player tells me, based on terrain, what they would like to summon and we 50/50 die roll to see if they get what they want (we are considering changing this to an ability check instead)
4. If they fail on this check we roll on my D8 random monster table to see what appears.
We've recently had a running joke in the game about summoned giant octopus in fresh water and how long they'll live.
Most amusing summon in recent weeks was a wyvern had grabbed one of the pcs and was flying off to its lair with him, the druid summoned 2 gaint eagles to arrive on either side of the wyvern to try to head it off at the pass so to speak only to see 2 summoned worgs fal to thier deaths. Magc is a fickle beast- but summon spells are IMO the mosyt troublesome spells in the game as written so I've come up with a "fix" that works for us.
The summon spells are amongst the most poorly thought out spells at lower level for their impact on play."The DM decides what creatures appears" being in the spell description would have cleared the matter up so much easier but alas we have what we have.
Stormdale