No one knows the future hold, so i can say it very possible for big coin like cardano will overthrow ethereum in the future but trust me it will take a long road for ADA if they want to do it, right now ethereum is more popular and more usefull than ada (according to me) but we don't know what ADA will do in the next few years.
this is true, who knows if ethereum will not be popular anymore in the future because other token or coin that's still not popular today.
but cardano is also really popular and being discussed a lot in youtube and the market of cardano is also quite strong as well.
right now whether cardano can overthrow ethereum or not is still unclear and whether ethereum will not be overthrown by cardano is still unclear too.
if its the market cap of both of this, it will change position a lot maybe when the market cap become close to each other.