From the stats I’ve seen it is more common for someone to sub during an offline stream than for someone new to twitch to sub. From my stats, the vast majority of new subscribers have watched the streams for some length of time first, and out of the very small proportion of users that are new to these channels an even smaller number are new to Twitch as a whole (and even then they might not actually be new to twitch). These are just from my stats though, so of course your mileage may vary. It also shouldn’t be assumed that anyone new to Twitch would be expecting fanfare when they sub in the first place.
From my point of view, more choice for the user in this aspect is a good thing, especially as it allows more privacy if the user wishes and also more privacy for the partner if they want to minimise bots abilities to snoop and gather data on subs. Also you mention it being more work now but seem to forget that twitchnotify has it’s own problems, for example it gives you a display name, which is not entirely helpful when their display name might be Japanese characters which forces you to jump through the hope of searching for that display name to find their username and twitch ID before being able to record the sub.