a) you really need to check out some case studies about things like this because people absolutely do not shift to a "better" or even "more complete" product. There is a thing such as lock-in and it's caused by many factors, some of which the user don't even have control over and
b) Consider that people using the other offerings could use your simple less complete offering but which has that 1 killer item (and a couple more as time goes on and you add them slowly). I have seen it many times and I'm sure you have too -- users keep using Photoshop but use that other editor for something special. Or use Office but use some other tool for their specialized offering.
I really think this is the way to go to a) have success and b) even get funding. It's incredibly difficult/rare, even for a team of multiple highly proven individuals, to get that kind of funding and green light to go do a waterfall project based on your hunch that everyone will switch if something just existed.
There are a lot of very smart people out there and $10m isn't too much for an experienced founder to raise. If this market is so big and frothy that you can name hundreds of low end competitors, someone would be competing at the high end. Why isn't anyone??
Once you can answer that, you'll know what kinds of avenues are available to finance it.
Sometimes, high end variants look seductive because there's no competition. But, there's no competition because margins are too low to support the high end product. Other times, there is no competition because sales cycles are measured in years and nobody can stay alive long enough to get to yes. Other times, there is no competition because you have genuine insight that gives you a severe competitive advantage.
Those 'choices' point towards three financing options. The first one, if margins aren't high enough to pay for the damned thing, you're starting a non profit, so it's time to look for grants, patreon, etc. The second one, where sales cycles are too long, is a great use case for crowdfunding. And the third one sounds like a deal that VCs would get in on (if you have the background/communications skills).
On the other hand, if you can't figure that out, or if you keep coming back to no financing, you might be looking at a bad idea...
2) There are fundamental reasons why you can make a better product and the leader can not respond (would be too long trying to outline why here)
3) This product is used by eng. daily most startups in this space are by software eng. and try to address the pain points for eng. and not for managers.
4) The leader product can not be used by F500 customer (managers) without a number of 3d party addons (which can and should be part of core functionality)
5) without going into specifics imaging SAP ERP system that was built from quickbooks e.g. fundamental mismatch between original arch. and what was bolted on over the years.