One of the main reasons I switched to Opera was the ability to have more control over the start page.
The biggest reason to switch to Opera now is the ad blocker is much faster than ABP/Ghost/etc and web pages load significantly faster now.
edit: apparently there are opera addons that allow you to load a custom page instead of the speed dial so that may also be a moot point anyway
When you open the start page, on the upper right corner you have a config button. Among other options there was "Speed Dial" check box. Is that what you wanted?
A cog which lets me 'Customise start page' but expanding Navigation and unchecking Speed Dial did not disable speed dial.
On the top left I have a Menu but the only thing I can see to do with speed dial is a button which opens it in a new tab or focuses a tab which already has it open.
I really just want a blank page when I open a new tab.
Opera 37 on Windows.