If it's Comcast, you have a provider that's starting to get closer to the scale of the old Bell System, just minus a lot of the unprofitable rural areas that Ma Bell served under Universal Service. Comcast absorbing Charter would make a telecom giant that could by economies of scale out-compete any competitor if it wanted to do so over time. I do believe that this would be tempered by the increasing proliferation of ILEC FTTP and 3rd party FTTP + 5G services on the low end.
If such a merger were to happen, I would imagine Comcast would be forced to divest NBC+Universal. Given that the new administration would be eager to see such a divestiture happen, I think we are within the realm of possibility for this.
Comcast by absorbing Charter solidifies its place as the cable company. Pa Cable?
Competition wise, I remain unconvinced that combining 2 cable providers that generally do not overlap, and generally are the sole provider in their serving footprints, changes anything regarding the status quo. Your already at an antitrust nightmare the way it is! Regulations still make it difficult to start a local-scale ISP. It's capital intensive and high risk. You do see a lot of new upstart FTTP providers popping up out of the pools of COVID-era broadband subsidies, but the majority of the country is stuck with a cable MSO as their sole HSI provider.
The challenge of somewhat differing technology stacks can be resolved, much like it was when Charter and Comcast bought Adelphia's hodge-podge collection of local systems. There is already some technical cooperation on the set top box side of the house.
Honestly, I'd prefer T-Mobile to stay their course and focus on wireless and dabbling on some FTTP trials of their own. Their 5G service is an important solution for the bottom-end of the market, people who just need basic connectivity at a very low price.