Should difficulty really be happiness based?

I've played a handful of games on max difficulty (won) and I honestly don't understand the appeal. There's one thing there being a challenge, but there's another being limited and thus forced to following the same old religion/SP/Ideology flowchart over and over due to the happiness cap. I found that the game was a complete grind-out, and for the last time played on this difficulty level, a chore.

I have much more fun playing a couple of difficulty levels down, and actually being in the position to consider which SP to pick, which religion to adopt, which ideology tenets to take, etc. Surely this game can be made more difficult and challenging through other means which don't have such a grave impact on your future options?

For instance, a production per turn cap wouldn't limit your options but would require you to build what you need less recklessly. A GPT cap would require you to spend more efficiently. Perhaps a combination of the two? There are just SO many ways to spice the game up without making it a grind-out!

For those who are a fan of the current setup please express your counter-agruements too. Remember though, I never said completing the game on max difficulty was an issue; just how boring it makes the game.

Highest difficulty level in the Civ series has always to straight jacked laced.
At the highest levels, building world wonders not advisable even if you can succeed,
Civ II & III both had extremely obvious optimum tech paths that you'd also need at the highest level.
(III even included at highest level the one beaker per turn tactic of most expensive tech for when you couldn't naturally research anything in a reasonable amount of time)

For Civ IV, the main limit on city expansion was increasing city maintenance costs. At the highest level what people would do here is REX 4 cities in careful placement that they claim as much territory as possible [choke points combined with keeping borders closed] and then in fill as the economy allows; often in waves.

Civ III in which the limit was corruption / waste of the furthest cities tended at highest levels to be an opening game REX / corruption and waste be damned, full speed ahead.
Civ II which was similar in early game but after mid game there were governments that eliminated corruption completely was also just like that on Deity.

No it shouldn't, It should be skill based. Go play some good human players.

Ok then... nerf order and let's see everyone pick freedom
Since people seem to love the happiness bonuses and worker's faculties so much... try doing without them for once.

Yes, it can be done. Yes, you can survive revolutionary wave on deity. Try it!