That's really a subjective question for which there isn't a simple answer. But here are some thoughts. One could make the argument that the first half of the decade brought us superior hits with longer staying power, as evidenced by the number of songs which held on to the No. 1 spot for 5 weeks or more... Call Me, Bette Davis Eyes, Endless Love, Physical, Centerfold, I Love Rock & Roll, Billie Jean, Every Breath You Take, When Doves Cry. (There may be others; I don't have the list in front of me now). But that's a matter of personal preference.
Maybe there would have been more songs reaching No. 1, but the timing just worked against them as they were competing with those No. 1's. I'm sure "Waiting For A Girl Like You," or "Rosanna," or "Open Arms" would have gotten to No. 1 had they been out at some other time.
Radio itself seemed different during both halves of the '80s. The first half was more or less still very much a part of the old Top 40 era. The Hot Hits formula started around '81, which basically condensed the Top 40 to a more restricted version of 20 or so tunes. But a repetitive countdown of the same songs over and over was the main feature. Just a theory, but hearing these same songs lends itself to familiarity which, in turn, might have led to their longevity at the top of the charts. Hot Hits and Top 40 declined by the end of the decade, replaced by more fragmented specialty formats, such as lite hits or urban. Even country witnessed a movement away from pop (Kenny Rogers, Anne Murray) to the more traditional sounds of George Strait, Randy Travis, & the Judds. It was not uncommon for a Top 10 from, say, 1981 to contain pop, rock, country, & R&B songs; not so by the end of the decade.
The dawn of MTV also provided a vehicle for that longevity factor, keeping songs in the public eye visually in addition to audibly on the radio.
Yes, 45's were available throughout the '80s, but they did lose ground to album cuts & CDs considerably. Many stores stopped carrying 45s altogether, making room for those larger CD cardboard boxes, cassettes, and what remained of vinyl albums.
Personally, I knew radio and music was changing for good by the end of the '80s. That was when a song hit No. 1 on the Billboard chart, "My Prerogative" by Bobby Brown, and I had never heard it. By that time, with Top 40 gone, people just gravitated toward their format of preference.
