I haven't had any trouble with the increased difficulty, but the new reaction system does seem a bit ham-fisted. We could instead give aliens higher TUs, firing accuracy, reactions, armor, etc to increase difficulty. Simply having aliens react every time takes the randomness out of it.
In vanilla there was a check where a triggering units Reaction Stat x Current TUs was compared against the the reacting units Reaction Stat x Current TUs. If the reacting unit had a higher rating they would react, otherwise they would fail to react. As a result if a sectoid had 21 TUs left he wasn't likely to react unless a soldier was using the last of their TUs and/or had really low reactions, even if the sectiod only needed 9 TUs for a snapshot.
The current system in OXC seems to reduce all TU costs for alien reaction shots by ~30% and allows them to react every time, removing the check. I haven't seen an alien not react until they have fired more then is possible with the weapon they are carrying. Maybe X-COM has a 10% chance of reacting if their reaction score is > 3.5 x the aliens? I'm not really sure what the criteria would be, it almost never happens, but I think I remember it happening under the current system.