The early days of Magic are "notorious" for the awful creatures present in the game.

A world of fast mana

A cursory glance across the card files for Alpha, Beta, and Unlimited (ABU) reveals a staggering amount of fast mana. Sol Ring, Mana Vault, Basalt Monolith, the Mox cycle, and Black Lotus all deliver an incredible amount of mana very quickly. This reality would almost certainly inform a large portion of design in the first four expansions.

Why were creatures weak?

I'd like to submit that they weren't. Not really anyway. Yes, instant and sorcery cards (to use the modern names) were substantially more powerful, but conceptually they could only be cast once. In reality the existence of Regrowth made the nascent four-of rule basically invalid. We see that reflected in DCI quickly restricting it three months into competitive play.

A card like Craw Wurm could be cast on turn two on the play. It would stick around and put the opponent on a four turn clock. Even if it only did six damage that would be over a quarter of the starting life total.

No, Craw Wurm never saw real tournament play. Competitive play was never the only, or even the primary, way people played Magic. To this day the most common and popular format people play is a pile of cards I own, played at my kitchen table. It's a certainty that the crew designing the sets would have been cognizant of this. Further, they would have known after ABU proved there was a consumer appetite for Magic that some players would spend hundreds of dollars to own the best cards.

Ultimately, then, the general power level of creatures was conservative rather than actively bad. The flaw was in over-estimating the primary draw back of instants, sorceries.

The Case for Lady Orca

Lady Orca is a much maligned legendary creature from the set Legends.

She is a 7/4 legendary creature for 5RB.

Compare it to a similarly massive creature from ABU like Force of Nature. 2GGGG for an 8/8 trampler that has an upkeep cost of GGGG every turn. Or all stars like Erhnam Djinn a 3G 4/5 with what was intended to be a downside of making your opponents creatures unblockable.

Today we see an overcosted vanilla creature. To the designers, Lady Orca in this format is a three turn clock with 0 the only downside being BR casting cost and Legendary supertype and it dodges two of the premium removal spells in the format (Terror and Lightning Bolt) and receives a chunky 7 life when hit with Swords to Plowshares. Compared to other creatures this is an insane rate.