I think arguing based on outcome misses the more fundamental point. The president is a citizen. When Angela Merkel speeds she gets a ticket, and when she goes to the supermarket she stands in the queue (which she actually literally does herself regularly, in contrast to Trump I suppose).

So regardless of whether banning him is good or bad in terms of exposure or whatever, he's a user on the platform and he ought to be treated as such. If Trump wants to speak as the president with authority I assume he has the white house press department at his disposal.