The GOP plans are basically age-adjusted flat grants of tax credits. Like all flat tax proposals they are highly regressive (the $12/hour foodworker and Warren Buffett get the same amount.)
but the GOP approach does respond to an ACA weakness - which is that all subsidies end at 400% of poverty ($47,000 for a single individual in 2017. Of course the current system provides a lot of other breaks:
* workers in employer-based plans pay low premiums and the entire cost is deductible by the emloyer. For them health insurance may be free - but family coverage may not be provided, worker contributions may be substantial, etc.
As Trump has now famously said: it is very comlicated. - gwc
How the ACA and GOP Health Plans Grant Tax Credits