MariaDB Parallel Replication Performance Tuning Issues - performance

Question

This is my first ever post so would appreciate some guidance. Situation is as below,
Replicating from VM A (Main Production Serer) to VM B (Slave used mainly for DB Replica and generating a few reports and also replicating down the stream to 2 other testing servers)
VM A Cofig:
32GB vRAM
8 vCPU (some Xeon CPU running at 2.4GHz)
1.5TB SSD
Windows Server 2012 R2
Production Applicaton running on XAMPP using Apache & MariaDB 10.1.38
VM B Config:
16GB vRAM
4 vCPU (same variant as VM A)
300 GB SSD
Same Windows Server 2012 R2 as VM A
Using the same platform as VM A- XAMPP with Apache & MariaDB 10.1.38
Problem:
No matter what settings I use, parallel replication just doesn't work like it should. Seconds behond master is continuously increasing. I've tried various values for binlog_commit_wait_count & binlog_commit_wait_usec as well but to no avail. At 1 or 2 combos, the group commit ratio increases a little but then eventually reduces again to <1.05. Settings for my.ini for the slave VM B is pasted below,
my.ini:
key_buffer = 8M
max_allowed_packet = 32M
#was 256M
sort_buffer_size = 16M
#was 2M
net_buffer_length = 8K
read_buffer_size = 8M
#was 256K then 4M then 8M
read_rnd_buffer_size = 16M
myisam_sort_buffer_size = 4M
query_cache_size=512M
query_cache_limit = 128M
#didn't exist, was 64M
join_buffer_size=128M
#didn't exist
thread_cache_size = 32
table_open_cache = 20000
#didn't exist
tmp_table_size = 256M
#didn't exist
max_heap_table_size = 256M
#didn't exist
log_error = "mysql_error.log"
expire_logs_days=30
log_bin_trust_function_creators = 1
slave-skip-errors = 1062,1060,1032
connect_timeout=100
max_connections = 2000
skip-host-cache
#skip-name-resolve
#innodb_force_recovery = 1
slave_parallel_threads = 4
#slave_parallel_workers = 4
slave_parallel_mode=optimistic
slave_domain_parallel_threads=4
slave_compressed_protocol = 1
#slave_parallel_max_queued = 131072
#slave_parallel_max_queued=16777216
server-id = 101
binlog-format = mixed
log-bin=mysql-bin
relay-log = mysql-relay-bin
log-slave-updates = 1
report_host=slave-main-replication-server
sync_binlog=1
#binlog_commit_wait_count = 30
binlog_commit_wait_count = 25
binlog_commit_wait_usec = 100000
innodb_buffer_pool_size = 8G
#was 2560M
#innodb_additional_mem_pool_size = 32M
innodb-buffer-pool-instances=4
#didn't exist
innodb_log_file_size = 256M
innodb_log_buffer_size = 64M
innodb_flush_log_at_trx_commit = 1
innodb_lock_wait_timeout = 50
innodb_io_capacity=1000
#default 200
innodb_io_capacity_max=3000
Any ideas would be appreciated. I've gone through dozens of posts and wikis and everything else inbetween of whatever I could find on the subject but none of them helped. I've tried setting "sync_binlong=0" as well, nothing happened. Is it just the CPU cores causing a bottleneck? I'm all out of ideas. Been trying to solve this for almost 2 months now. Please help.