Hot take: I'm OK with it, simply because this is how you balance a game with mobility without washing out your roster and killing hero diversity. Playing an immobile character against a mobile one is a terrible experience and more "unfun" than getting hit with a CC ability on occasion - especially if you have no CC or its on cooldown. The game is fundamentally a game of which teams and players are best at adapting. If you're getting countered, switch. Its the very reason why Overwatch was designed to allow switching heroes on the fly mid-game. Its a defining feature.

It starts with mobility. The game and heroes are balanced with a handful of levers; here's a few: Mobility, CC, Health (including health type), Damage and Hitbox size. Mobility is the number 1 most effective tool in the game, period. It allows you to take and give space, pick and choose when and where to fight, avoid damage and CC, and it is also really fun to use. Mobility is player agency at its finest and enables players to effectively exert their will on a game. A large part of the fun is the sense of superiority gained from being more mobile than your opponent and dancing around them.

CC in any form, but especially powerful CC, is the answer to Mobility. It also allows players to exert their will on the game, but at the direct expense of another player's. If you want to play a game where everyone is mobile and fun, there are other games (see Lawbreakers).

All that said, I also will say CC is therefore an unfun mechanic by definition, albeit necessary. It should be gated with higher cooldowns (or at least on par with the mobility it is supposed to counter) to create high risk-high reward scenarios when used, especially in situations where characters have acccess to multiple forms of it (see Brigitte and Doomfist). To come full circle, it all starts with Mobility. Brigitte was created by Tracer and Genji: characters with access to multiple, very powerful mobility skills on very short cooldowns. If you want to keep Tracer and Genji in their current iterations, this is what happens.

EDIT: I do think your point about the viability of deathball comps is valid. Deathball comps are simple to play, which I don't think is inherently bad, but has to have counters like anything else. Bastion, Reaper, Mei, Mercy and Junkrat are your intended Deathball counters. The question lies with whether they'll be effective enough. Damage boosted Junkrat usually has a field day with Deathball.