Cotoneaster tree with persistent disease?

Got a cotoneaster tree of a variety I am not sure of that was planted in the garden before I moved here that is infected with a persistent disease (possibly fire blight or bacterial canker). It manifests as dead new growth that is particularly noticeable at the moment. I have tried to counteract it with cutting out the effected branches in previous years but it has impacted the tree again this year with the over all appearance of the tree looking very unhealthy. The flowers are still attracting bees but the leaves and shoots on the top of the tree are looking very diseased and dead. I have already lost a young tree planted nearby that is likely to have caught the same disease from this tree that is not doing well. Am I better off just killing the diseased tree and planting something that will use the space better and if so when is the best time to kill off the unhealthy cotoneaster? Thanks for any advice or opinions.
Happy gardening!
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COASTAL SOUTHERN ENGLAND...silty-sandy-loam ravaged by wind