Why are most High End Amps class A

I do not believe that actually to be the case. As to your question, no , you are unlikely to find an amp that will be unquestionable better than your Mac at that price. You could look at the Pass amps in the 150 range, they will have a different sound than the Mac which you may or may not like better. One of the mistakes most commonly made in audio is to think that you will find an amp that does everything better than the one you have. Unless you have a terrible amp this is almost never the case. Every amp regardless of price is a product of compromises and will possess different virtues. If you like the sound of what you have and it drives your speakers well do not change until you have heard something you like considerably better. I have owned and been a dealer for several class A amps in the past but do not own any now and do not foresee buying any in the future. Class A is not a cure all , it is one technique for achieving good sound, there are others. I would listen to a particular amp regardless of its design and evaluate it on its performance.

Good advice from Stanwal.

Making sure the amp can drive the speakers properly is the most important factor. Most else is subjective judgement regarding what sound best.

As Stanwal wisely states, listen before you change. I have owned a McIntosh 2105 for 10 years, and during that time also owned a Mac MC 300 which I sold after 3 years to buy a Pass Labs X250.5. For most efficient speakers, at modest volumes , that amp will run in class A. I used it with 3 different speakers, and for my taste, the Mac 2105 was better in all aspects. The point of course is that you may feel differently, but do not make the mistake that I made and buy on the opinion of others and their taste - try it first.

Class A amps run at full power when idling. So if you really want a dual use machine (home heater, and amp) then go for pure class A.
I have a small 50w 'class A' amp, and love it. I would never buy a big class A because of the heat, and strain on the electrical system.

Most Class A amps are higher priced, and not necessarily higher end. Due to the high heat output, most class A amp will need higher quality parts and much more expensive case work to dissipate the heat, thus resulting in a higher cost.