Wither breaking too mutch blocks causng major server lag and preformace issues

I just vibing at a lifesteal smp trying to be nice to kill all the withers someone spawned it in a fair way not with admin abuse to make spawn good for new players but i notice a issue when the wither is is below 50%heal they do his second phase but he mining down causing many blocks appear that causing lag and preformace issue and he doing the charge attack making it more worse and making more block entieties causing more lag so i have to force using admin commands to delete blocks before its crashing devices and cause problems

Its so bad that even my grapics getting ruined