They claim about 60% of GOP votes. That translates to about 20% of all voters are hardcore MAGAts. Even if that number is rounded up a little, I would say at least 15% are the rabid Trump supporters you are talking about. That’s roughly 25M people. That is not an insignificant number of people. Then there will be a ton of other votes for Trump and the GOP simply because some people will vote for their party regardless.
Now in THEORY I could agree with you that having a party push for low taxes and small government isn’t bad. But the GOP hasn’t believed that in decades. They might still campaign on that message because who doesn’t want their taxes lowered, but there is absolutely nothing “fiscally responsible” about that party and every time they gain power, they prove that.
And that is my personal biggest worry is that if Trump somehow doesn’t win the GOP nomination, some other Republican could step up and start singing the same “lower taxes” bullshit that they’ve been trying for ages but ultimately when they get power they will try shoving religion down our throats, cut abortion rights even further, cut taxes - but only on the ultra wealthy, which will leave the rest of us with even more massive deficits - and increased spending on military programs we simply do not need.
Republicans have proven time and again that they do not deserve support.