I am not an expert of this field, but if they say so now, it is probably true. Don’t forget, that Firefox is open-source, so everyone with some knowledge can judge, whether Opera can beat them in some sense or not.
“the reason is because it’s slower than Vega”
I may not be expert on the first one, but that is just one misleading claim you made. The reason is, that IN SOME CASES it does not beat SW Vega, which has very different meaning compared to your claim.
“affecting the entire program and it shows”
Sure. It does not suck as much as it used to… :P