Ravens hadn’t gone 6-1 in 7 straight games since SB47. Yes, the defense was playing well, but to say they would have “easily” done something they hadn’t done in 5 seasons does not make sense to me.
I'm a Flacco fan, and think it's plausible that the Ravens go 6-1 down the stretch last year with him... better passing game, team healthier, easier schedule, reliant on the defense.... but I agree with you that Jackson and the improvement in the running game was a huge part. The Ravens were a horrible running team (and there was no commitment to running) with Flacco at QB in '18. I think the gains in the running game helped the defense.
That said, Gabe used the wording, "... could have easily...", not 'would have easily," and there are big differences in the choice of could or would.