Some good points, Comparing 2 different bikes with 2 different riders is one thing, but it falls down when you properly compare 2 different bikes with the same rider.That's not a phrase I like, "Starter bike". It implies a sub standard machine which has to be upgraded at some point in the future whereas anything above what we term as a BSO is more than capable of taking you from one end of the country to the other, will not put you at a disadvantage in any fish& chipper organised by one of the local clubs that a bit of extra training wouldn't overcome and is all you need for even the most demanding sportive. Sure, an extra two grand spend will get you a gain, but the law of diminishing returns being what it is only a marginal one. If you're a snail on the climbs you'll still be one no matter how light the bike is and if you are struggling to break evens in a 25 a top end TT bike won't put you under the hour.
All this entry level nonsense is a media invented thing in the wake of the "New Golf" boom, when middle aged fashionistas with high disposable income are willing and able to splash out four or five grand on an ego trip. Good luck to anyone who can do that, but it skews the perceptions of what you actually need to compete in and enjoy the sport. As someone once said, it's not about the bike. Something brought home to me last year when a lady on a Tiagra equipped Moda with unbranded wheels and tyres blew me apart on a climb.
I am noticably faster and more comfortable on my new bike than my first bike. No question about it.