Thank you for your message.
It's all very confusing. Are you thinking a downgrade in package from M350 to M125 would improve things? Would this be with the Hub 3 still?
M350 and M125 are still on DOCSIS 3.0 using bonded downstreams and bonded upstreams, although for HUB3 there are less streams bonded together than GIG1 off a HUb4 or HUB5.
DOCSIS 3.1 itself is inherently better latency than DOCSIS 3.0 but only if VM did a specific firmware upgrade to the CMTS which I'm unsure they actually did in the end and various areas still have different CMTS manufacturers (Arris/Cisco/Nokia). The old River Delta (Motorola) CMTS that had the single thread download speed issue a few years ago should have been replaced by Arris or Cisco kit by now.
Also DOCSIS 3.1 in most areas is under utilised compared to DOCSIS 3.0 as majority on HUB3 still and they don't use DOCSIS 3.1.