No two offices are exactly the same (I've worked in a good handful) so that's the extent of my knowledge. I'm sure some on here will offer advice when they only know the four walls they have worked in for the last X number of years. Or they once worked in one other office many years ago and therefore can speak with that knowledge.
Bullying can take many forms. If you are asked to work your day off or complete on a given day some will see that as being asked to do too much.
However, some will not have solid commitments and are therefore not all that bothered about giving the company an extra bit. Some offices will have managers that ask for a bit today but then give a bit tomorrow (like a manager that asks you to work a day off (for OT) but then gives you two days off together next week as a thanks). If you're the give and take sort of person it could work. I'm sure some managers are all take and I'm sure some staff are zero give (both with solid reasons for their position only they can justify). Then there are the rest of us just muddling through.
No one on here will be able to say if working for Waitrose will be any better or worse unless they happen to have recently quit Waitrose and are now working on delivery (or vice versa and still happen to be posting on here).
If you like the idea of walking 20,000+ steps per day and working generally on your own outside all day and in all weathers pick RM. If you don't like that or think driving plastic boxes (heavy with food and drink) to different people's houses and unloading them seems better pick that. I'm sure both have there good and bad points. Personally I can eat pretty much what I like and not gain any weight. However, I feel like collapsing some days. The office in the morning can be stressful but once I'm out I'm generally my own boss (or pretend to be). On the other hand I think if I banged a Waitrose van someone would notice. However, good luck spotting any new damage on the beat up thing I drive around in for RM so if a wall jumps out and hits it I can claim it was done earlier. Swings and roundabouts.
Good luck.