What specifically leads you to this viewpoint?
All analysis of the Sorcerer I've ever seen, including my own, together with my experience of them in play. There was some claim that on GitP they "believed otherwise", but searching that found nothing, so if there is stuff that's showing how the Sorcerer is actually solid-to-amazing rather than "meh" I wait to see it.
Seeing the sorcerer class played at the table, leavened my own quite negative view of the class.
I've seen a bunch of Sorcerers played, and they've been significantly less effective than other casters played by the same players (including, very specifically, Warlocks in at least two cases). Wizards are almost ridiculously more effective, especially ones with good subclasses. One of the characters was an extremely effective character - but it was in spite of being a Sorcerer - most of his effectiveness came from being as Changeling with high CHA owned by a player who was really keen on this idea - but a Rogue with Expertise in social skills and a decent CHA would have been more effective in most situations.
The lack of versatility, seriously limited spell-list, the fact that metamagic isn't what it used to be, together with terrible base AC and little ability to use either cantrips or weapons to do decent damage between spells all piles up to make a class that's only "okay" on a good day.
And again let's be clear - this is 5E.
Sorcerers are not "trash" in any real sense. The range between the strongest non-exploit-y characters, and the weakest "basically optimized" (i.e. highest stat in primary etc.) characters in 5E is relatively small. I'm not saying "people are dumb to play them" or anything of the sort, lest anyone put words into my mouth. They have quite a lot of style and flavour, and support a much wider array of spellcaster archetypes from fiction than 5E Wizards do.
So they have a reason to exist, but I feel like their design is a weird hangover from a previous edition where they were spontaneous casters and Wizards weren't. I think someone else said similarly. If they had significantly more versatility, both in spells known and spell-list, that would be the main thing that would improve them, I'd suggest.