Q.pruning an old bottlebrush that was neglected decades
It is probably an old Calistamon viminalis. I am considering removing it and planting something else or even another one. It is perhaps 4 to 5 meters not much ‘body foliage’ and high straggly with other shrubs intertwined. Can it be pruned hard at the timber and will it sprout form there to make a decent specimen in due course or will it die or remain a few limbs sticking out? It is flowering at the moment, with all of 5 red bottle brushes.
Here is this websites article on pruning bottlebrush. https://www.gardeningknowhow.com/ornamental/shrubs/bottlebrush/pruning-bottlebrush-plants.htm
However, it may be easier to just start over with a new plant. A radical approach is rejuvenation pruning - cutting back an entire plant to 1-2 ft tall. This works for many shrubs but Callistemon's response is "iffy". In other words, it may die instead of sending of new growth. If you decide to selectively prune it back over several years, don't prune out more than 30% of the leaves in any one year.