Not so fast.....

Ripple current is the flow of current in and out of the capacitor as the voltage changes across it. There can be no voltage change without current flow (charge added to or taken from the capacitor), that's just how they work.

Yes, the ESR directly affects the ripple current rating, since heating is current squared x resistance. But, so does surface area, which dissipates heat, etc. Because of the square factor, ripple current is the major issue with heating.

Heating is the primary factor in lifetime. Yes there are other factors, but heating tends to cause shorter life. If heating is too much, life will be "very" short

. Each manufacturer has a formula for lifetime vs ripple current, voltage, etc. Ripple current is a "proxy" for heating.

Number of capacitors definitely affects life vs ripple current. With one large capacitor, all the ripple current goes through that capacitor, and so through it's ESR.

With several capacitors of lower value adding to the same total uF, the ESR may or may not be different per capacitor, or even for the total, but the surface area total is a lot more, allowing better heat removal. The net ripple current rating is the sum of all the parallel capacitors.

You may have noticed that capacitors for SMPS often tend to be long and relatively thin. That maximizes surface area, and minimizes the length of the heat flow path, for good cooling. "Dissipation" is not the issue, "heating" is. If you can keep them cool, their ratings increase.

When you replaced the 4 capacitors with a single one, the ripple current rating of that one had to be equal to the sum of the 4 that were in there before. If it is not, the lifetime may be considerably shorter.

If the ESR of the one is the same as each of the others, the dissipation will be 16 times higher, since the ripple current is 4x higher.... the one capacitor has to handle the current that 4 did before, and it has to dissipate 16x the heat.

Presumably the designers of the thing did the calculations, and used 4 capacitors because they were needed. Your "redesign" may or may not be sufficient.

I'd be betting there may be an issue unless you did the design work and know the one can do what is needed. Or unless the load on the VFD is sufficiently lower than the design maximum load that the ripple current will be much lower than the original setup was designed for.