Depending on your Company they may not even have bought an annuity and it is being funded by current contributors and large top ups from the Company itself. If not the annuity will have been purchased and cannot now been altered. Had you had a defined contribution scheme and bought an annuity yourself and not had any health conditions declared at the time, it could not be changed later.
In most cases the DB is better as it pays an increase every year and pays a spouse pension of 50%. Had you bought an indemnity and asked for a spouses pension and annual increases of a specific % it would greatly have reduced the monthly payments you receive.
Annuity rates have also been very low over the last few years.
When I retired 16 years ago I recall my pension pot being a little over 200,000. My DB pension is now £21,000 pa. If I was buying an annuity with that amount today I would receive around £12000 pa, as a ball park figure.