No, mRNA was suspected to be viable, but it was never proven. Like most new medical developments the early tests showed it didn't work and those needed to be worked around. Some believers did the research to make it work, but they had their detractors who said they were wasting there time as the problems weren't solvable. This time the detractors were proven wrong, but there have been other cases where more effort was put into something with no result (at least so far?)

Afaik, it was backed up behind a lack of safety trials.

Given how expensive those are to run, and how mRNA's primary benefit (speed of development) wasn't a competitive advantage in "normal" times, we had something that we thought was better, but no financial case to toss the gobs of money at it to get it certified.

If SARS-CoV-2 is remembered for one thing, it should be for finally breaking the logjam and "giving" us approved mRNA platforms.