To reply a bit more fully to your query re different people's roles during labour -
All the midwives I had were brilliant. However their main role is to monitor you and baby's vital signs and guide the physical/medical aspects of labour along. They have to do a tremendous amount of paperwork on your vital signs during labour so they won't be totally free to support you or your partner. In the early stages of established labour you will probably see several midwives, whoever answers your buzzer. This can be a bit disorientating.
You probably won't see a doctor much. I saw them for a few minutes on their 12 (?) hourly rounds, when I got an epidural and when I finally had to go to theatre.
I think the labour can be quite tough for partners. We ladies experience it through a fog of (natural or otherwise) chemicals but they are faced with the full on reality of it. I know my husband was very worried for me during labour, tired and scared. It was a great help for him to have our doula there to reassure him that everything was progressing normally. It was also good that he could have a nap or nip down to the hospital cafe knowing I was with her.
The role of the doula is to support you as the labouring woman, not just look after the medical aspects of the care. During my labour my doula spent a lot of time helping me focus and manage the pain positively. When I was pushing she was right there saying ComeOnPushPushPush! Exactly what I needed.
You say they are a complete stranger but it didn't feel like that to me at all. She had visited several times before the birth so she really knew my wishes and I trusted her. Everyone one else in the hospital was a complete stranger so having her there in addition to my DH was wonderful.
She also visited a couple of times after the birth to help with breastfeeding etc. She was the person I called when panicking about anything after the birth.
Do not underestimate the value of this continuity of care, it is so important.
So, basically, I love doulas. We should have many more of these wonderful people 