Nvidia's own pe ratio is around 80 it looks like. Its not actually that insane. Overvalued? Maybe. But all this is saying is that basically, you think that your current required rate of return minus your expected growth rate for ARM is around 1.7%, and your required rate of return is going to be pretty low right now because interest rates are so low. You value future earnings more and you think it's going to grow a lot. You might be wrong, and for a company like AMD with a pe ratio above a hundred you might be betting in an awful lot of growth happening, but in this environment, these are not "insane" numbers.
What you brought up above in this thread is how expensive the acquisition looks as a multiple of earnings. That multiplier is the price of the company vs the earnings for the company, which is literally just a simplified P/E ratio that ignores dilution etc. You may be thinking of revenue multiple based valuation instead?
