Oddly, Gretzky's shooting-percentage in 1985-86 (his lowest between 1979-80 and 1990-91) was still higher than Ovechkin's in every season of the latter's career, excepting two ('19 and '20). Ovechkin is a very high-volume shooter.
If you look back at Wayne's 1985-86 season, his goal scoring and shooting percentages were definitely down a bit earlier in the season, but not excessively so:
Games 1 to 23: 18 goals in 23 games (shooting percentage = 18.6%)
Games 24 to 49: 20 goals in 26 games (shooting percentage = 16.0%)
Then, he suddenly had the longest goal-less streak of his career:
Games 50 to 58: 0 goals in 9 games (shooting percentage = 0.0) [37 shots on net in this period]
Games 59 to 80: 14 goals in 22 games (shooting percentage = 15.4%)
I suspect that during that 9 game goal-less period, Wayne realized he was in a bit of a goal-funk and he just decided to try to rack up his assists totals as far as he could. Not that he wasn't trying to score goals, of course, but I think the point of breaking his own 135-assist record and the challenge to get as many assists as he could sort-of entered his mind around the start of February.
From 1983-84 through 1993-94, in general, it's very typical that Gretzky scored more goals in the first half of the season than the second.