In my opinion, that kind of thing is wrong because it tends to overcentralize the metagame: Say, if you were running a deck that aimed to do its thing during the midgame, then you basically had to own a few titans in your colors (or wurms), or you wouldn't stand a chance against decks which did pack those cards, making them expensive as well, which would act as a deterrent for newer players who can't afford higher-end cards.
Having a bunch of cards that are good but not one-size-fits-all would help keep individual card prices in check, and also allow deckbuilders more chances to build their decks differently, placing further emphasis in the skill required to decide on one of the many available cards that gives you more of an edge in the current metagame you plan to take on with that deck.
I'm not good at analyzing individual MtG cards, but I'd say that the stronger cards are the ones that give you as many choices for as few risks as possible. Say, like how Cryptic Command gets to do an awful lot of stuff for 1UUU, or how Snapcaster lets you recast any card in your graveyard with an attached 2/1 body on top of that. Also, toning down the value you get for your mana over time means that they can experiment a bit more with spell effects, like how Counterspell was too strong at UU and constricted the design of "worse" variants to 1U or less, while Cancel at 1UU gave designers more leeway to work with (2U, UU, 1U and U), or how Shock rather than Lightning Bolt allowed them to fine-tune how much damage and/or added effects you'd be getting on top of your baseline 2 damage for R at instant speed.
1. I think if Wizards fills the creature pool right, the theoretical 6CMC cards I'm suggesting wouldn't always be the game ending threat the titans proved to usually be. They could help lock it up, but they don't HAVE to be the end of the world. I'd like to think the 5CMC creatures wouldn't be too far behind in power level. Even something like Huntmaster at 4CMC was awesome way back when. People could build decks that don't have 6CMC or 5CMC at all if the power can be spread properly across the 4 and lower tiers.
However, the haymakers don't have to be creatures. They can be anything. I still say Elspeth is a modern-day titan. Planeswalkers are totally viable finishers.
My problem is that since the titans, they seem to be scared to print anything of consequence at 6 CMC in higher numbers. Landing a huge threat is empowering. It makes you feel like you're doing something devastating. But people are winning now by Pack Ratting and Master of Waving and Fleecemane Lioning all over the place. It just doesn't have that same feeling to me right now.
This is why I'm so disappointed by the Gods. What a letdown.
2. In terms of your price issues, make them available at rare, or even put them in intro packs or something, and give Mythics a reason to exist. Let's stop using Mythic as a limited balancing mechanic and instead create unique cards that do crazy shit.
3. I personally don't think Counterspell was overpowered at UU. I think it was the crazy amount of other counters they printed around it that made it seem that way. Things like Mana Leak are busted. Counterspell forces you into heavy blue. UU is pretty restrictive. Countering spells is something they've really cut back on in terms of power, though.
4. Cryptic should have been UUUU. And even then it's probably still too good. I do, however, think it's funny that most of the balance issues you're talking about there are blue. Shock vs Lightning Bolt is really a call by Wizards on how they want to build Standard, btw. We'll see Bolt in standard again someday.