I think it depends on when the ability triggers that it can be countered. Maybe he’s trying to guarantee that he doesn’t waste his mana on something that can be easily negated. That is Seglagg’s style to have some kind of backup plan lol though the threat of walking ballista makes him a target now...

Edit: I think I have a Walking Ballista IRL that I pulled from a pack ^^; I remember being a little sad I pulled it instead of Yahenni

How it would work ideally is you cast walking ballista. Then if you have any etb triggers (which you don't rn) those happen, then there's a trigger for every +1/+1 counter you remove to deal 1 damage to any target. What's important is Elek currently has 6 servos, a Yahenni, and a Marionette Master whose current power is 2. Seglagg has 12 health rn, and Elek can sacrifice 6 servos to Yahenni. Each time you sacrifice an artifact, target opponent loses life equal to Marionette Master's power. So here's how a turn where Walking Ballista is cast would go down:

Seglagg casts Walking Ballista. On the stack- before it enters the battlefield, Elek can sacrifice a servo to Yahenni. Unless someone else has an ability to cast, Elek can keep doing that on the stack. Seglagg dies before Walking Ballista enters the battlefield.

How this is going currently is that Seglagg is making a lot of threats that are scary, but marginally less scary than Walking Ballista. He has a full board, he's drawing about half his entire deck, and with that liiittle life gain of 4 life, he'll effectively be out of kill range for Elek. That's why Elek wants time to think things through before Shamanic Revelation resolves.

Also you pulled a Ballista and got disappointed? At current market value, you can buy about 12 yahennis with a single ballista. Walking Ballista is currently $15.50 for a single card

That makes sense!

Yes I was disappointed because I don’t play competitively and didn’t know the value of its abilities. I’m really really casual with MtG. I wanted Yahenni because of the MtG stories. Obviously by now I see how good a card ballista is but at the time I was a little disappointed, yes. shrugs

Oh okay that makes sense. Yahenni is pretty rad, and yet so many people underestimate how good they are. Though if you still have the Ballista and you don't want it, selling it would be a very very good option because it's worth so much. It's stabilized to about $15-$16