They're hard to compare. To me, the gold standard of RTS campaigns is SCII: Wings of Liberty, to give a frame of reference. The original Halo Wars had a bunch of varied objectives, but for the most part, it boiled down to "build up a death ball and win"; the only time you'd need to change that attitude was on the occasion when you needed par time.
HW2 I think requires you to be a lot more proactive, partially because it adopts multiplayer scenarios into campaign objectives (which is overall fine, although I wish it didn't straight up use the same multiplayer lines) and because it forces you to split up your forces more and juggle different strategies at once. It's got more variety in the mission objectives, although I think it still doesn't manage to have some of the inventiveness and breadth of WoL. I also appreciate that it spends more time telling the story in-game rather than relying on cutscenes, although again it still feels like it could have been pushed further.
So if you're a base economy/macro RTS player, HW2's campaign is probably a step down from HW1, but then again Halo Wars has streamlined the economy aspects significantly by design so the series probably isn't the best fit anyhow.
I definitely think that the difficulty curve is better in HW2 as opposed to having the hardest missions in the game be in the second Act, though it seems like Legendary has way more leader spam than is probably fair.