A gaming mouse should be tailored to a user's hand. That means a slanted one handed mouse. The entire point of the exercise is to get a mouse that is suitable for YOU, not "suitable for everybody".
Ambidextrous mouse is definitely not on the list of requirements for being a gaming mouse, and if anything is one of the factors that will work against said mouse when being selected as a good gaming mouse.
Full disclosure: I haven't used ambidextrous mouse in over 15 years and I will NEVER use one again now that I'm used to one handed mice. I'm also the key target audience for the sellers, and buy high cost premium mice, my current one being Logitech G700s.
I actually ended up dragging my mouse to work when I wasn't offered a proper right handed mouse there. Ambidextrous models are simply far too uncomfortable once you're used to a proper one handed mouse.