I think to move this conversation forward I'd need to see some historical examples of what you're talking about. Most of the powerful noncreature decks I remember from across Magic's history were only possible because Wizards didn't know how to correctly cost mana ramp, card draw, or resource conversion cards (Cadaverous Bloom, Necropotence, etc).
The old conundrum of magic the gathering was that you generally couldn't get both tempo and card advantage at the same time, so you would have to generally cater towards one school of magic or the other.
Now, this isn't 100% (what is?); there were printings like
ancestral recall that let you have both tempo and card advantage at the same time, and ETB creatures have existed for a long time, but as a whole, it was hard to get both simultaneously.
Generally speaking, creatures were very purely focused on board presence, and just terrible. No one really understood just how bad they were. When I came back to magic in 2006, I was utterly shocked at the creatures WOTC was printing, because many of them seemed so much higher power than what was considered a "bonkers" creature when I started the game.
I came from an era when
juzam djinn was considered a design mistake,
hypnotic specter was nuts, and
serendib efreet, was considered a top notch threat. 5/5s for 4 or 3/4s for 3 without a real drawback was forbidden fruit for a long time in the game as far as creatures were concerned.
These are all really laughable by today's standards, and pretty tame even for Ravinca's (it took me a while to understand this). Again, generally speaking, a creature was a square board presence defined by its stats, maybe with an activated or triggered ability, and a spell was a spell. You didn't merge the ability to generate tempo and get ahead on spell castings, and you certainly didn't tie it to a credible source of board pressure.
Creatures were generally bad compared to spells, and Wizards had spent over a decade trying to figure out how to fix their creature problem (hexproof, shroud, and protection were common tools). Around ravinca you start to see better ETBs. To put into perspective how volatile this period was, the previous top tier threats were the kamigawa dragons, which featured LTBs, and depended on the old legend's rule to sort of duck tape together a crude combination of board pressure and spell velocity upon the second legend's casting, powerful enough to generally win the game on the spot (e.g. koko's 10 point life swing).
Note this is also the period where tap out control is born, largely off of the back of the power level of moluko and keiga. Why sit back and play this delicate control game, when you can run a reasonable card advantage strategy, while at the same time asserting pressure. This is pretty revolutionary.
After ravinca you have Time Spiral with ETB and than Lorwyn, and the printing of the first planeswalkers, with a steady increase in ETB creature density. At that point, even a control deck can now assert pressure (e.g. modern nahiri decks) with ultimates, as well as getting a free spell casting every turn, allowing midrange and control decks to both assert pressure, generate tempo, and generate card advantage at the same time. Time spiral->Lorwyn also gives us our first degenerate tempo deck in the form of faeries, which is basically an ETB pressure deck, generating both tempo and CA off of
ancestral visions,
spellstutter sprite, and
mistblind clique. Also, some card called
bitterblossom.
From that point on, ETBs just became steadily more and more insane (thragtusk, titans) and planeswalkers more pushed and dominate (jace), which brings us to today.
Now, I agree commercially this was a smart business move, and there were some net positives.
It was a reasonable solution for creatures being occluded by spells, as well as giving midrange some reasonable teeth to fight against control decks. Creature focused games tend to have a constant flow, are easier to visually process, and tend to have constant action with keeps player's engaged. Planeswalkers are exciting, powerful cards, that feed into that. They also keep games reasonably short, since you have constant pressure. They were not idiots for doing this, and I would have done the same thing, were the choice presented to me.
The problem though, is that breaking that original symmetry, makes spells a lot worse. Why would you play "just a spell" when you can run a "spell creature" that largely does the same thing, but can also pressure the opponent. Casting a "plain spell", in magic the gathering, can actually put you behind. That sucks.
On the plus side, when they attach multiple spell effects to a spell, that seems to help a lot in keeping pace with a game's tempo. They did that recently with sphinx's revelation and it was awesome, and they seem to have done it with this life gain WOG. These are all good things, and I hope to see more of it.
)
