Eiyuu senki is a lot more vanilla. Painfully vanilla at times.
Honestly Sengoku Rance isn't that crazy strategic it just has a few curveballs and time limits that keep new players on their toes before they know how to abuse certain characters and passives that trivialize even the hardest mode.
And yeah Rance is a hard character to sell. I like it as a chance to play "evil" anti-hero characters for a change, but not everyone is into that. The sex scenes are pretty squick, I just skip through them and play the games for the plot, unironically.
Eiyuu Senki difficutly is very much the "ramp up enemy health values" type though, with the expectation that you're using NG+ stuff for higher difficulties. It's big problem, as the other anon mentioned, is that AI is completely hamstrung in it's ability to actually send strong attacking forces, so you essentially never lose ground once you take it. It's primarily a puzzle game in that regard, figuring out the puzzle of how to complete the game in as few turns as possible, not because the enemy is ever actually threatening.