Eh, there is a lot to unpack here. Namely the notion that Germany was some kind of super power by 1939 which it absolutely wasn't in any sense. Other than that, this is basically two questions bundled as one.

1. Were the conditions of the Versailles Treaty not harsh enough?
2. How was Germany able to prepare for an offensive war so quickly?

I've answered both of these questions repeatedly before but never really explained how they tie into each other so here we go I guess.

1. Were the conditions of the Versailles Treaty not harsh enough?

Oh yeah, they were plenty harsh. Germany did initially make a serious effort to keep up with the original payment plan but the allied powers weren't the only ones demanding compensation from the German state. German industrialists also demanded compensation for industries lost or occupied by the allies. To keep this post reasonably short I won't go into depth about the absolute clusterfuckery that is Weimar era economic policy but Germany relatively quickly resorted to increasing money supply (MS) which lead to inflation and subsequently hyper-inflation and a collapse of the entire Germany and Austrian banking sector.

Enter the Dawes plan. Again, not going into the details here but it was basically a renegotiation of the payment plan of german reparations and a resolution to the Franco-Belgian occupation of the ruhr valley. An important part of it was loans, mainly from Wall Street. With fresh hard currency entering the German economy and France and Belgium no longer occupying the crucial german coal deposits in the Ruhr something interesting happened. The French steel industry suddenly faced a coal shortage whereas the German steel industry did not. Combined with fresh money the German steel industry rebounded and came to dominate the continental european market by the mid/late 1920's.

The came 1929, the wall street crash and the Young plan. Again, not going too far into details here but basically it further reduced the German war debt and postponed payments in an attempt to mitiagate the spread of the great depression to europe. It didn't really work but it meant that Germany paid even less of the original debt. So much for the economic part of the treaty of Versailles. The TL;DR is that between the restructurings of the reparations, German unwillingness to meet the payment schedule and American loans which Germany would later default on it might actually have been possible that the Allies paid more to Germany than Germany paid the allies during the interwar years.

As for rearmamant, well, Germany basically violated every stipulation of the Versailles treaty by keeping arms production secret and moving it abroad. In addition to this the armed forces were secretly expanded and the stipulations of the treaty either cleverly circumvented or ignored.

2. How was Germany able to prepare for an offensive so quickly?

Well, much of it is covered above. Circumventing the treaty of Versailles. Another part is financing all of it through the use of some very clever accounting. So creative in fact that it is probably the single largest and most audacious violation of every rule and law in economics ever pulled off. The famous MEFO bills was, in very simple terms, a second kind of currency introduced and used to finance rearmament without it affecting the governemt budget. You can't just invent money like that of course, well not long term anyway, but you can apparently do it in the short term provided you have a plan for how to pay for it later. In the German case, the plan was to use gold reserves and other assets from occupied territories. It worked, sort of, through the annexation of Austria and Czechoslovakia, the occupation of Poland, the low countries, Luxembourg and finally France. This provided the German state with continued means to fund the war.

However, this did in no way mean that Germany was a super power at the time. It was undoubtedly better prepared for the war because it had spent years preparing for it but it also relied on no small portion of luck, allied lack of preparations, outdated allied military planning, allied appeasement and some insanely dangerous gambles that, had they not worked, could well have ended WW2 a lot earlier than it did.

To give you just one such example, french reconnaissance aircraft actually spotted and reported the German concentrations of armor and vehicles in the Ardennes but the reports were largely ignored despite the french Armé de l'air having an ample supply of bombers. Had they struck the German units in the Ardennes the result could well have been the almost complete destruction of Germanys only armored spearheads as they were lined up along the roads basically bumper to bumper for miles and miles with no room to maneuver or seek cover.