Alonso is getting a lot of heat for basically showing the reality of the "mighty" Honda power. Everyone expected Honda and Mclaren to struggle to get to grips with the new engine regulations but not for them to be this bad. Poor PR and overconfidence has led both companies to be completely lost instead of facing the facts. Honestly they should be more concerned about making a good PU rather than naming them and turning them into some ridiculous cartoon.
I agree with him, whenever I hear someone say "ALO is the best driver on the grid!" my first thought is "what have they been smoking?". He's the biggest jerk on the grid, that's for sure. He showed his true colors some years back when he blocked HAM in the pits during qualifying while they were both at McLaren. Since that day he's had a permanent hold on the title of "Brandon's Least Liked Driver On The F1 Grid".
Just my opinion of course, nobody has to agree, but I despise him.
I think far too many people hold a grudge against Alonso for that reason and I'm not really convinced it's justified. However, the notion that Alonso isn't better than 50% of the grid - which is what the person you quoted was actually arguing, and not that he's the best - is baffling to me. Bias aside, he's one of the top drivers in the sport. There's far too much evidence of that and far too little evidence suggesting otherwise.