Each micro inverter does have its watt limit, true. But if the watt limit is the same as the panel it is connected to, well it won’t peak shave.
Wholesale solar(.Com) shows the warranty of the enphase iq7 and iq7+ as 25 years.
So, design how much kWp you want, both ways. Then consider the future. Adding panels to the enphase system is no problem. Just add one or a dozen, it does not matter. But adding panels to my inverter is impossible, it’s already maxed out. I have to get another inverter, then I can add more panels.