The Seals logo isn't from the 70s, of course, being from 1967.
The two trends I identify with the late 60s and 70s are:
1. Extreme minimalism, as in the Canucks, Flyers or Flames. (See also, the Sharks, Nationals, Stags and Blades in the WHA, and to a different extent the North Stars and Nordiques). The Flyers obviously did that best as far as coming up with an identifiable mark that was suitable for the various things a sports logo is used for, but I don't think the Canucks did it too badly. I wouldn't miss it if it was gone, and I think the biggest thing it has going for it is that the team never did manage to stick the landing on anything better. Great logo approach if you can nail it, it's not always easy.
2. Stuff in a circle. Hate it. I don't understand why anyone likes the logos originally used by the Islanders, Scouts or Jets, and the Sabres logo is just OK (at least there's some design harmony in the way the animal is placed between the crossed swords. The Penguins logo is much better without the circle, and the Sabres could probably look better without it too (a company called Celsius did a concept in the mid aughts with a front-facing bison head above crossed swords and no circle - the illustration was typical overworked 90s stuff, but the concept was on point.) There's nothing quite like the very first Jets logo, which is apparently a defenseman getting turnstiled by a plane, Mario/Bourque-style.
The original Seals logo is an absolute car crash that manages to combine the worst aspects of minimalism (it barely looks like a seal at all) and stuff-in-a-circle (the elements have no harmony whatsoever, and if you just glanced at the logo at a distance it'd look like nothing other than a dull green circle with some white bits on it)