We need to realize that in these days of technology, few serious divers rely upon mechanical analog watches.
The mechanical analog watches of today tend to be worn by "desk divers" who occasionally get in the pool or in the surf. Few of us really have a need to track our air supply or depth.
That being said, some of us prefer sporty dive watches like the PO or the Sub but Omega designed the 300 MC to be a nostalgic "desk diver" suitable to be worn on a variety of occasions. The thin bezel and tiny pearl of the '57 original were impractical for divers of the day and grew over time and only reappeared on the 300 MC to remind us of its heritage.
Likewise, the bling of the shinny bezel and PCLs are not practical for serious divers unless one is seeking to catch the eye of a shark or barracuda.
We have to accept the 300 MCs for what they, and for what most of us, are: desk divers. Desk divers want a watch that can be worn on the beach or in the board room. That is the targeted market of the 300 MC.
An automobile accident in 1979 ended my SCUBA diving but I still hang out at, and in, the pool. And glancing down at the 300 MC on my wrist reminds me of time spent in Florida springs and the blue Caribbean.