You need 2/3 to propose an amendment for ratification via a constitutional convention, but the actual ratification requires 3/4, so it's even harder.

It also makes for some weird power dynamics due to extreme imbalance in state sizes. Specifically, we're at the point where the top 1/4 (i.e 12) most populated states together contain 60% of the population, and the remaining 3/4 contain the other 40%. Thus, if small states gang up, they can arbitrarily amend the constitution while representing a minority of the overall population - "tyranny of the minority", if you like. And then consider the fact that it's state legislatures ratifying amendments by a simple majority vote, not residents - which means that, in practice, the 3/4 of the legislatures voting to ratify might actually be representing something like 20% of the population. Then account for gerrymandering etc on state level, and it can be even smaller.

FWIW, the Founders themselves were well aware of problems that can stem from an arrangement like that. When Hamilton was explaining why the principles underlying the Articles of Confederation couldn't be sustained long term in Federalist Papers (#22), one of his arguments went thus:

"It may be objected to this, that not seven but nine States, or two thirds of the whole number, must consent to the most important resolutions; and it may be thence inferred that nine States would always comprehend a majority of the Union. But this does not obviate the impropriety of an equal vote between States of the most unequal dimensions and populousness; nor is the inference accurate in point of fact; for we can enumerate nine States which contain less than a majority of the people; and it is constitutionally possible that these nine may give the vote."

And further noting that even the power to veto can be very detrimental if abused:

"To give a minority a negative upon the majority (which is always the case where more than a majority is requisite to a decision), is, in its tendency, to subject the sense of the greater number to that of the lesser. Congress, from the nonattendance of a few States, have been frequently in the situation of a Polish diet, where a single VOTE has been sufficient to put a stop to all their movements. A sixtieth part of the Union, which is about the proportion of Delaware and Rhode Island, has several times been able to oppose an entire bar to its operations. This is one of those refinements which, in practice, has an effect the reverse of what is expected from it in theory. The necessity of unanimity in public bodies, or of something approaching towards it, has been founded upon a supposition that it would contribute to security. But its real operation is to embarrass the administration, to destroy the energy of the government, and to substitute the pleasure, caprice, or artifices of an insignificant, turbulent, or corrupt junto, to the regular deliberations and decisions of a respectable majority. In those emergencies of a nation, in which the goodness or badness, the weakness or strength of its government, is of the greatest importance, there is commonly a necessity for action. The public business must, in some way or other, go forward. If a pertinacious minority can control the opinion of a majority, respecting the best mode of conducting it, the majority, in order that something may be done, must conform to the views of the minority; and thus the sense of the smaller number will overrule that of the greater, and give a tone to the national proceedings. Hence, tedious delays; continual negotiation and intrigue; contemptible compromises of the public good. And yet, in such a system, it is even happy when such compromises can take place: for upon some occasions things will not admit of accommodation; and then the measures of government must be injuriously suspended, or fatally defeated. It is often, by the impracticability of obtaining the concurrence of the necessary number of votes, kept in a state of inaction. Its situation must always savor of weakness, sometimes border upon anarchy."

"It is not difficult to discover, that a principle of this kind gives greater scope to foreign corruption, as well as to domestic faction, than that which permits the sense of the majority to decide; though the contrary of this has been presumed. The mistake has proceeded from not attending with due care to the mischiefs that may be occasioned by obstructing the progress of government at certain critical seasons. When the concurrence of a large number is required by the Constitution to the doing of any national act, we are apt to rest satisfied that all is safe, because nothing improper will be likely TO BE DONE, but we forget how much good may be prevented, and how much ill may be produced, by the power of hindering the doing what may be necessary, and of keeping affairs in the same unfavorable posture in which they may happen to stand at particular periods."

Reminds you of anything?..