The cost difference is ~$0.30 - $0.40/w. For example the 16.5kW ground mount we did was (36) 460w panels tied to a $1500 11.4kW inverter. $1500. Let's add up all the stuff we would need for micro inverters. (36)IQ8M @ $180ea = $6480; (36) connection cables @ $20ea = $720. Combiner Box $500. $500 + 6480 + 720 = $7700. $7700 - $1500 =
$6200 for a difference of $0.37/w. $0.37/w is not a small difference.
AND then there's wire and line loss. This ground mount was a ~200' run. With a string inverter it's ~30A at 380vdc. So 8 runs of #10 ~$400 in wire. With micro inverters you need 48A at 240v. So ~400' of #3 for ~$1000. So that's another ~$600 in wire. PLUS when the string inverter is saturated at ~11.4kW the line losses are zero.
The customer I'm helping has a ~9kW ground mount with micros but no smart panel. He wants batteries. It's going to be cheaper to AC couple his micros to a hybrid inverter. He'll have ~$5k in redundant equipment because his installer didn't want to hire people that knew how to add panel voltages.... his system also isn't online because another corner they cut was understanding which areas require production meters and which ones don't
Another benefit to string inverters is flexibility. We repaired a hail damaged ~12kW ground mount that used M215s. It would have been great to use newer, better panels to increase the capacity a bit but we were locked into what was compatible with the M215s. So we installed refurbished 260w panels when ~340w panels would have easily fit for about the same price.
... AND... system expansion. We've got ~3 expansion projects in the next few weeks taking advantage of some $0.23/w panels. Adding ~12kW to one system. Panel cost is ~$3500. The micros alone would be ~$6k. But since we're just oversizing an existing inverter the cost is $0. Sure... a lot of generation on a sunny day between 11am and 3pm will be lost but there's almost no value to that these days anyway. What you want is to double production in the mornings and evening.
.... sure.... if you wanted to ignore cost every panel would just have it's own embedded AC inverter. But if you're going to go down the road of ignoring cost we'd all just be using nuclear power and not fuss with batteries or solar.