I'm always been a bit torn about marketing. I've been pretty adamant with startups in the past to not focus too much initially on marketing but asked them to be very aware of needing it down the road. 7 or 8 years ago there was a lot of back and forth on just how much marketing is necessary for startups and when. Brad Feld and Fred Wilson both wrote about it and started an interesting discourse (I just linked to a couple of their posts....Google if you want all of them). Fred kind of went on a tear against it but ultimately backtracked a bit to sharpen his statement, making clear he was talking about the companies they invest in and wasn't generalising. My take on all of this is that you won't be able to avoid marketing...it's simply a matter of when.
This doesn't need to be a long, drawn out post on my point. It's enough in my opinion to say that if you are successful with your product, you will eventually need marketing. The more successful your product, the larger the budget you should plan. Initially, get as much marketing for as little spend as possible. This is where I totally agree with Brad and Fred. Once you are scaling the business though you won't be able to avoid spending heavily. Once the competition gets wind of you, and they hopefully will if your product is that good, the fun begins. They will start tearing into you and your product. They will start making claims about what they can do and you can't. They will have larger stands at the conventions and more money addressing your customer. You need to start early enough to be able to keep up and make sure you get your message out there. This brings me back to the quote that "Perception drives Reality!" Ignore it at your own peril.
When it comes to European startups I've worked with or am working with, business plans that go out into year two or three of a scale up always underestimate the need for marketing budget. Especially when it comes to enterprise software, you will need to put your stamp on the map. The US companies will have oftentimes a factor of 10x or more when it comes to their budgets. How can you possibly compete if no one knows about you? Further, their product may not even be as good as yours but they will get to your customers first and lock-in is often far more difficult to break than simply getting in the door first. Make sure you budget properly for marketing and if raising capital, be prepared to defend the amount in your business case if VC's question why that number is so high. There are good arguments for it.