From what I know, explore teams are basically challenge and quest teams from that kingdom with one troop randomly replaced or something like that. So these teams do often have some natural synergy (especially the challenge teams, unless their most important team member gets replaced). It also depends on the kingdom, of course.
I myself spent the last few days in Maugrim, Zaejin, Stormheim and Adana. I can’t say I’ve noticed much of a difference to how these places were before - but Stormheim and Zaejin were always the more dangerous of those places because of the possible base teams. I ran into a team of Valkyrie, Mercy, Zephyros and someone else and it almost wrecked me because I wasn’t paying much attention. Also random Mythics can be annoying, depending on how many traits they get. But overall… different kingdoms always had different difficulties and I have not noticed an overall increase.