"Coin flippiness" is not a measure of a prolonged time period in Vintage as defined by your "eras" as you've clearly noted a lot of the problem decks have fairly quickly been restricted. Its short periods of time in which a singular problem deck arises that is simultaneously powerful and finishes the game in the first 2/3 turns of the game. I initially highlight decks because of this, and latter highlighted the entire time period of 2000's as that is the time period in which many of these cards found their way onto the restricted list for this very reason. Yes this is a very broad time period, in which I highlighted decks that were of "different eras" as you call it, but a lot of this transition was caused by changes in the restricted list (and some new printings / erratas).
The Chalice+Lodestone Workshop deck was the only coin flip deck that saw a long period of dominance due to Wizards inaction during the time period. I feel this was much more of a result of Wizards not really caring about the format at that time, more so than Workshops being less of a problem than the combo decks. Shops of course also gave players the illusion that they had a chance to get out of their mana lock. Countless arguments by people talking about playing Spirit Guides + Ancient Tombs to break their mana lock...
You bring up Misstep, Mindbreak trap, and the other ways to interact turn 0 with a storm deck, but arguing for these cards is really not that different from players that expected people to play Spirit Guides + Ancient Tombs to beat Shops. The number of cards that interact meaningfully on turn 0 are very few and far between. This creates a tremendous burden on the deck builder to constantly be cognizant of those archetypes.
In our current metagame, PO is on the slower end when you compare to these historic decks. However, it is still very capable of a turn 2 kill and seems geared to go off around turn 3/4. That puts it on the same speed as a game 1 dredge deck. These are the types of combo decks that are good for the format. They keep opponents "honest" so to speak, but don't necessarily force your opponent to play a short list of cards if their deck is fast or controlling enough.
You boil it down to two competing ideas:
In general, having more viable deck choices in Vintage is a good thing.
In general, being able to play games of Magic where both players get to play spells and make meaningful in-game decisions is a good thing.
One involves a greater number of choices in the deck building process, while the other concerns itself with a greater number of choices during the actual game. However, unrestricting these cards that incentivize turn 1 kills are bad for both points. I think we are in agreement that it affects (2) in the sense that the game is over quicker and therefore there are less decisions. It also affects (1) in the ways I just highlighted above. Forcing a player into playing Force of Will, Mental Misstep, and Mindbreak Trap to interact is not a good for deck building. In the same way that forcing a player to play Ingot Chewer, Ancient Tombs, and Spirit Guides to interact with the dominant Workshop decks was not good.
On a separate note, I pointed you to the articles on general magic because they highlight that this is a problem throughout magic. Not just in Vintage. The problem is just exacerbated by a format where turn 1 is more crucial than in other formats. The article on the Mothership discusses the disadvantages of being on the draw for turn 4/5. A point in time which the difference that they boil down to 10 vs 12 mana. In Vintage though we are talking about a difference that is more like one player actually playing cards, while the other player is just sitting there. More than any other format, we should be wary of cards that are pushing us towards these games where one player literally does not get to play a single card from their hand.