When thinking about balance people need to think about these things:
Why is Chamber picked? Because people like his guns and TP.
Why are Cypher and Killjoy NOT picked? Because chamber does their job just as well.
Nerfing his trips is the change that works best for everybody, now chamber players can still enjoy the attractive parts of the agent, while Cypher and Killjoy players aren't completely overshadowed.
And to address the whole "chamber is a sentinel" thing, Riot has stated that there is more than just 1 type of sentinel. there are setup sentinels like Cypher and Killjoy, who hold space through place-able gadgets, reactive sentinels like Sage, who hold space with slows and reactive abilities, and force-based Sentinels, who are particularly strong opponents when they are within their setups, IE chamber.
This is why his trademark nerf is a good change, pro teams and ranked players alike now have to make a decision when picking a sentinel; do we want more firepower with lesser flank watching and push stopping in chamber? or do we want an agent who has less firepower, but is better at holding flanks and stopping pushes? Before the nerf, chamber was best at both.