I can agree to this, but only to the extent of what I've seen, since I have yet to play him myself. I've played plenty of Normal games against a Sol (I didn't lane against him, though) and he just got slaughtered by our mid laners. (One game was LB, another was Yasuo, and another was Zed).
[start /Rant]: Just now, I lost a ranked game because someone on my team chose him mid lane into a Yasuo and let's just say...Yasuo ended the game with 14+ kills and only 3 deaths (give-or-take a few as I'm typing this through memory alone). For the sake of everyone's Ranked games, I wish people would stop trying Sol in them so early into his release. Like, he hasn't even been out long enough for anyone to get even decently good with him. [My opinion; I'm aware it isn't 100% factual and that there may be maybe a few players who've learned him] And if there are players who have learned them, can you please find some way to be the one that makes it on my team, because losing games solely due to a new-ish champ feeding (I'm sure it's unintentional, since you are probably learning him still) isn't fun. [end /Rant]
But, yeah, from what I've seen, he could use some power-ups. A lot, actually. But, to be truly honest, his kit seems to be very balanced, compared to previous champ releases. That's probably why he's so weak right now. He's almost literally what we've all been asking for, in terms of balance, but now that we see it, it's hard to accept and use it.