It seems to me that they could have made
the -10 line real mainframes (no, IBM and the BUNCH did not consider the
-10 line real) with just a little effort and not much money.
--
DEC through the 'golden age' didn't go after that market. They tried to
target scientific rather than corporate computing.
If you look at the sales numbers of their 36-bit systems, they were tiny
compared to Univac, Burroughs, and IBM.
The engineering and field support costs required to compete with the big
iron companies to the level that big-iron buyers demand would have consumed
all of DEC's resources at that time (through the mid-70s).
One of the things that isn't talked about much is how the PDP-6 just about
killed DEC because of all of the resources it consumed to get it out the door.
They did eventually abandon their 'fan base' to go after the corporate
market, and that was the beginning of DEC's downfall.