Not exactly. There's a reason WebKit saw wild adoption by all sorts of projects, while Gecko adoption stagnated. The Mozilla codebase is still too complicated for most people.
Arguably, though, even if Gecko's code base were taken down to be smaller and easier to use than WebKit (and I have no idea how it actually compares today), it would be at a tremendous disadvantage because so many projects have incorporated WebKit.
If I want to use WebKit in a new project today, I can find a ton of people online who have done so in the past and use their experience to get me through it. If I want to use Gecko in a new project, I will have a considerably smaller amount of outside experience to lean on.
Not exactly. There's a reason WebKit saw wild adoption by all sorts of projects, while Gecko adoption stagnated. The Mozilla codebase is still too complicated for most people.