Sales will throw money at anything with a clear ROI. If you can reliably say it'll make salespeople 1% more effective, then that's an easy decision. If you look at Chorus.ai / Gong.io / VoiceOps - these are new sales tools that have really burst into the market.
That said, as a result of this, there is a lot of tech in both of those domains. Your customers will have a lot of tech and be bombarded with a lot of options. Is is very noisy and confusing. So it gets harder to get above that noise and stand out. Particularly in the early days.
So even in those cases, I think starting out in a niche can make sense (A niche of startups can be a good one for a bunch of reasons). Simplifies your approach to the market.
Marketing budgets are huge, but the barrier to entry for creating another SaaS marketing tool is low.
If you yourself are looking to start a company, the easiest thing to do is figure out what advantages you have that other companies don't have.
If you have a proprietary advantage in a crowded market, then don't worry about the competition and focus on telling your story to your customers.
But I would avoid entering markets that have low barriers to entry and where you don't have a proprietary advantage, simply because you want to avoid markets with high barriers to entry.