These new features are really awesome! They make my phone run really hot and it can crash sometimes. Maybe there should be a setting to remove some of these features as to not bloat the app.
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Do not forget that this is the first of many betas to come that will progressively improve and polish the OS before public release. Between now and then, Apple will surely improve the way the system handles these new features in messages, as well as every other new feature that was in introduced. Come September, I highly doubt they will ship software that crashes and overheats the phone. It will be better.
Also, you need to think about the demographic that Apple needs to aim for. There are many young teenagers who own iPhones who love features that allow them to get colorful or expressive with their messages. The new generation loves to share everything with everyone, and they have naturally gravitated towards apps that allow them to do it in creative or fun ways. This is largely why Snapchat is such a popular social medium for millennials.
I'm not sure of your age, but this messages app clearly caters to people who are younger, eccentric, and creative. All the teen girls who text their girlfriends saying "OMG look at this video Stacey posted to Facebook last night!" will probably love using the "loud" or "slam" bubble effect, because they will recognize that it more accurately expressed the emphasis of what how they're trying to convey their tone. They also love using emojis, too, which explains why they emphasized expression via emoji in this new app. I'd say give it a month or two after release for the younger users to get comfortable with the idea of using these and it'll become mainstream.
Long story short: people prefer to message over call. The more animated and expressive you can be over message, the closer we'll come to a culture that will all but eliminate calling all together.
Just because it's not for you doesn't mean it's not going to get its share of use. All it takes is one viral meme/video/use-case for these bubble effects to become a hotly used feature amongst millions of iPhone users.