Yeah, I understood what you said, but I cannot understand why Intelligent Systems designed the "higher difficulty" like that. If anything, the higher difficulty should be less based on chance in order to more tightly design the challenges.
Intelligent Designs likes to implement really stupid game design in the most difficult difficulties. To be fair, its not really meant to be fair or all that fun. Its clearly a masochistic difficulty for players who find the game normally too easy.
Despite this, if you've planned out how you aim to tackle the game mode in advance, the whole randomness aspect is manageable in my opinion. It just means you have to power game from the get go (eg. use tonics, promote units early to get rallies, Panne is actually good).
That's really the thing about the more difficult Fire Emblem game modes. It becomes a game of accounting and management basically. Like, if you're playing Hector Hard Mode and not save scumming, I don't think Cog of Destiny can be completed reliably without Pure Waters...which you have to go out of your way to buy 8 chapters earlier.
The whole unavoidable bullshit issue is generally limited to specific maps in the early game. The only two on the top of my head are Shadow Dragon's Chapter 1 and Awakening's Chapter 2.