This thing about entry-level bikes is a favourite topic of mine and I have to stop myself from trolling these boards....
It's ALL MARKETING. The bike brands show these bikes that cost ten or twenty thousand pounds. The bike media, not knowing what else to talk about, promote these stories of super expensive bikes. The youtube channels also need clickbait so they talk about it too. As do magazine reviewers and so on. And before you know it, that 10k bike has become the standard by which other bikes must be judged. The bike brands do not care whether they sell these "halo" bikes; alll they want to do is get htier brand being talked about and increase prices through-out the range, thus increasing the average price at which a bike is sold. Bingo! And have you ever noticed there are so many "bike brands"? Why's that then? Because it's relatively easy to make a bike frame. But there are far less groupset manufacturers right? Only Shimano/Campagnolo/SRAM; there's a high barrier to entry. Making a frame is far easier - not saying it's totally simple, but the barrier to making/selling one is easy: if you're an independent and cannot make carbon frames due to setup costs, then make a steel frame and everyone will think you are cool. Are you a big company? Great, so make carbon frames and try and convince everyone that your frame is better than the next guy's frame. If you haev a big marketing budget, then you get more brand recognition and sell more frames. Bingo!
There is a caveat though. Generrally speaking, the more expensive frames are better than the cheaper ones. I have a cheapo bike, current list price is £300. I also have a pricier bike and the difference is huge. But then there is the law of diminishing returns. Comparing a £300 bike with a £600 bike leads to large improvements in the dearer bike. Comparing £1000 bike with a £1500 bike, the differences are there but not as noticeable.
So I'm just gonna give a quick answer here which pretty much alludes to what the others have said (that you shouldn't worry about what experts think. Well, except for me of course, as I am an expert.
Today, in 2021, if you spend £800-1000 on a bike, you're doing a-ok. You'll have strong wheels, a lower end (but stronger and sturdier and longer lasting perhaps) groupset from Japan (those guys sure are a reliable bunch). Then spend £2-.300 on a few tools/clothes/shoes. Ride your bike for a few months, you may have a couple of problems, learn to fix them. Then once this covid goes away, spend the reaminder of your money on a little cycling holiday. So for your £1.5k, you get a great bike, some tools that will last years, some bike clothes to make you comfortable, and a holiday whose memory will last a lifetime.
Now then, how about "entry-level" golf clubs, hifi systems, cushions. (Ok, just joking about the cushions
).