Short answer; no.
Long answer;
Ampipods turn cannibalistic towards the smaller individuals if there is not enough food. One of the main food sources for amphipods are copepods. So if you have too many copepods, it will eventually cause the number of amphipods to increase. Until copepod numbers cannot support the amphipods. After that they will turn cannibalistic and cut back their own numbers. So no you cannot have excessive number of them as amphipods will start to limit their own population as well as the copepod population.
In my mature tanks, the stable pod populations I have always been copepods and a smaller number of adult/large amphipods. There is also a small number of inmature/small amphipods but that population is either very small or transient. I think the adult amphipods puts a large pressure on small ones, so small individuals can only survive if adult numbers drop. Once that happens, some small ones reach adulthood and cutback the smaller population. A nice delicate balance.
When I mono-cultured amphipods for my marine betta, cannibalism was one of the main problems. I had to separate big adults from the culture as they would eat the "baby" amphipods.
