OK. Seriously. Just got done playing another Solasta fight - Level 10 characters: Paladin, Barbarian, Sorcerer and Druid. I also had Arwin Merton in the party (so basically like a Halsin kind of companion who is only temporarily in the party. He's a fighter with 2 weapon fighting). Tough battle against Soraks including a legendary one.
Number of rounds: 6
Number of reaction popups (excluding Paladin popups during the paladin's regular turn which Larian could manage those types of Smite attacks just like Battlemaster Maneuvers, so they don't count): 2 (both AOOs, and the Paladin's Smite was included in the same AOO popup, so it was 1 popup for both AOO and Smite for the Paladin)
There was also an enemy mage on the battlefield, but I killed him pretty quickly. If I hadn't, he might have triggered Counterspell reaction a few times... maybe...
Conclusion: Although popups COULD get a bit disruptive IF the circumstance line up just right, in Solasta they aren't very disruptive. 2 reaction popups in 6 rounds with a party of 5 (including Arwin) and roughly 10-12 enemies including 1 mage and 1 legendary is not bad at all.
I'm back to leaning towards Camp Prompts and less towards Camp Presets.