The founding fathers of our country believed in many things. They wanted all kinds of things depending upon their interests and the interests of those who supported them. "The Founding Fathers" were far from the monolithic group-think construct which people seem to want to lump them into today for expedience sake. Some of them believed in more limited government, some believed in less limited government. Most of their beliefs were derived from their experiences with totalitarian governance where citizens had zero say in their government. The degree to which any of them wanted some sort of governmental presence was debated hotly back then as it seems to be today. But it cannot be separated from the fact that they were coming from the whole of human history where humans were mostly subjugated with little say in how they were to be ruled.
I would say that above all, most of those who voted to ratify the constitution wanted a system of government the functioned well and was controllable by the citizens of this land rather than the vast power interests which controlled the governance of the rest of the world.
"Laws today seem to favor bigger government"
The laws of our nation reflect the overall changes in our country. Our population has soared from a maybe 2 1/2 million when this country was founded to 320 million roughly today. The needs of the people change. The needs of our country change. The laws of the country change. This is all a reflection of life and the evolution of our country. The complexity of our country, with greater population, technology, modernity necessitate a government more appropriate to the expectations of our people. Such a government will only logically be bigger than 1776 or 1876 or 1976. It is simple logic that the size of a government that was tailored to a country of rusticates with rudimentary technology would not be the right size government for a technologically advanced society that leads the world economically and militarily. It can't be any other way nostalgia by those who never have had to live in 1776 aside.
However, even so, what remains the same for our country and throughout its history is the set of rules that the game is being played on: "The Constitution". It is still there doing the same thing it did back when Benjamin Franklin thought that the grand experiment might not last 5 years. The Constitution, in fact, has stood the test of time and the strength of its ideas have proven to be powerful enough to spread throughout the rest of the world.
"Also the separation of powers is becoming less separate as legislators are giving the executive branch more discretion in enforcing the law"
How so? The separation of powers as defined by our Constitution are fairly hard coded. The constitution has not changed and the balance of powers is therefore intact.
Certainly there is an ebb and flow between which branch is the most predominant throughout our history, but the powers given to each branch remain the same.
Explain how the legislators done anything in giving the executive branch more or less discretion in enforcing the law.
"When the president says he will act on his own where Congress does not act, and Congress applauds him, they make my point for me."
That makes no point. There are at least 2 problems at the root of what you are hinting at. One is that there is a large component of politics and has been going on since before the beginning of the country. Two is the the problem of lack of clearcut approach to regulatory enforcement. Neither of these is some sort of constitutional dilemma.
The constitution places the president at the head of the executive branch where in modern terms the president has become and organizer and prioritizer of often conflicting enforcement regimes. There is both a lack of formal or standardized mechanisms for enforcement and a concurrent politicization of enforcement. And for the last 40 or so years there has been a steady emphasis not on enforcement of laws and regulations by the president, but on increasing regulations for political expediency for both parties with very little actual executive oversight of laws and regulations being put in place. This is not new or something that has cropped up recently. I would submit that the rush to deregulate additionally lends a shoulder to the idea that laws and regulations need not be enforced. Nobody has really sought to fix this problem in the slightest.
But aside from all of that mire. the constitution certainly allows for presidential discretion in the enforcement rules and laws to a degree and there really hasn't thus far been any attempt by congress to pass any legislation to clear any of this up. Each party seems to like lots of leeway for their guy in the Whitehouse.
Teddy Roosevelt held the position that the president could use any and all powers that were not specifically denied to him. He made the modern presidency what it is today as we have grown to understand it. There is nothing new here.