Last season was the only season both played a full year in the same league, right? So, off of that season:
Bruno: 18 goals (9 penalties), 12 assists, 95 chances created, in 3110 minutes
Grealish: 6 goals (no penalties from what I can see), 10 assists, 81 chances created, in 2184 minutes
So, when you factor out pens, and take into consideration that Bruno played 926 minutes more, I fail to see a huge difference. People rating Bruno higher is understandable, but I don't get why it's laughable to think Grealish is worthy of being in on this discussion. If he hadn't of missed all the games he did, judging by those stats, he probably would've overtaken Bruno in them all except penalty goals.
Also, yes, Bruno's influence in helping establish us as a top 4 team cannot be denied, but you can't underrate how Grealish not only saved Villa from relegation, but had them fighting for a European spot before his injury.