I do think they will be the rotation, as you say. Matchups, injuries, resting guys, etc..will dictate they do this anyway.
What will be interesting to watch is how long it will be those 6 guys doing the rotation. The health of Hays and Santander, as well as the stamina of Mancini will dictate a lot of that.
However, I think O's management want to see Mancini play a lot of 1B because it makes him more tradable.
Getting 6 guys regular playing time in 5 spots in not that hard. Each guy just gets a day off every 6 games. Plus injuries will cause time off for some players.
Per Fangraphs he was 9 for 15 on bunt hit attempts. He also was successful 4 of 5 times on sac bunts. Pretty nice ratios in both regards.
In his previous 2 seasons he was 4 for 13 when bunting for a hit, and 4 for 6 on sac bunts.
Looking around the league, I do see some players who bunt pretty often and have success rates over 50%. César Hernández, 39 bunt hits over the last 5 years (2nd in MLB) at a 57.4% success rate; Rougned Odor, 30 bunt hits (4th) at a 53.6% success rate. The median success rate for the top 30 in total bunt hits is a bit over 40%.
So, do I think Mullins could bunt as often as he did last year and sustain a 60% success rate? No. But is it a really good weapon in his arsenal? Yes. He’s really, really good at it.
Without the bunt attempts I come up with .232/.285/.384 for last year. But I think the bunts will always boost those numbers a little, though not as much as last year.
The OPS projections I’ve seen on Mullins have him between .637 (PECOTA) and .689 (Steamer). That’s a reasonable range to guess, and if Mullins falls in there, he’s not a starting OF. But he’ll get some playing time and we’ll see if he hits better than expected.