The stated inverter loss you mentioned is a bit simplified. A deeper look will allow you to make the best decision given your usage patterns, which is different than everyone else's. This may be especially helpful for you as you think about adding lithium, because there are differences to lead-acid that aren't so obvious until you dig deeper. Efficiency wasn't a stated goal in Gary's post, but I presume he doesn't want to waste energy/money.
We've been living full-time with our full-boat inverter system for 18 months. Every single AC device aside from the 2nd Skylla-i Charger is wired to operate via our Quattro 5kw inverter. We routinely run the scuba compressor for an hour via inverter, with no problems. I believe the Bauer Junior II compressor has a 3x inrush current, so even 6.6kw inrush doesn't cause issues with our Quattro 5kw. Over the past 18 months, I've worked at optimizing both power production and usage. Based on those optimizations, we went from running the genset and charging our lithiums every 3 days with 200amps to now, not running the genset at all on anchor and as I am typing this at 11am, finding ways to burn off the excess solar energy to keep the batteries from getting above 90% SOC. We are running the dishwasher/washing machine/etc at the highest temp setting to burn off the excess energy.
We nearly eliminated our genset usage and ran every AC appliance aboard, efficiently, through a bit of research. It may be tempting to apply rules of thumb, but the danger if it's wrong is that it leads you to making bad decisions. Here's what I've found, which may be helpful to you and to others:
Under section 3, they talk about efficiency vs. load. This is for the Victron 3kw, but since Victron states that the Quattro and Multiplus are mostly the same internally, let's assume it scales, just with beefier components and therefore higher numbers. The Victron inverters seem to hit above 90% efficiency by 100/3000 = 6.67% of rated load. For us, that means we run the Quattro 5kw for all uses except low load items like the computer, projector and LCD. For those, we use the 800w Mastervolt inverter that came with the boat. Note also I would suggest installing a simple $5 switch to turn off the inverter when not in use. Our Quattro draws at least 40 measured watts when idle, so that $5 switch saves us 40/26.3*=36AH a day alone.
Regarding genset load, our A54 came with the Onan 11KW MDKBN. Luckily Victron tested this very genset and based on the data, we can deduce that it's not necessarily best to run at full load. The efficiency curve starts to flatten out considerably around 5kw, which is less than half load for us. Further, I recall from the Onan documentation that for maximum longevity and reiterated here by Mastervolt and Fischer Panda that running above 70% reduces genset longevity. For us, our 120a Quattro + 80a Skylla=200 amps of charging (which admittedly we don't use much anymore) puts roughly a 5.2kw load on the genset which puts us in the sweet spot with respect to specific fuel consumption and most emissions measures while maximizing longevity.
Also, I think you are confusing inverter output and charger input - when Gary talks about a 4kw inverter, I believe he is talking about the inverter AC output, not AC charger input. For example, my Quattro is called a 5kw inverter but that means it can output 5kw AC from the inverter. The charger portion is only 120amps, which is roughly 120*25.6= 3kw draw from genset or shorepower when charging my batteries. It's important to understand the difference in order to size the system correctly.
With respect to the hypothetical 62 amp deficit if he were to run a 100amp (~2.6kw) charger with a 4kw inverter, there are a few more things to think about:
1) I have never run a 4kw continuous load for more than say 20 minutes. As you mention, the loads are only for a short period. Even with my aft AC, the duty cycle is really less than 40%, which means an average load of only 600w. With the washing machine, the full current is drawn when the water is being heated, which isn't for too long.
2) If you were to somehow find a way to use 4kw continuously all day, you will find that your inverter will likely heat up and reduce output, per the curves on the Victron white paper.
3) If you are intending to go lithium, the 62 amp deficit on say my 450AH system would mean the batteries could make up the 62amp difference for over 7 hours at 4kw peak usage.
I know everyone has their own energy needs, but we've found after some thinking and tinkering, that with our usage patterns and system, we're very happy to have the inverter run everything on the boat.
2007 A54 #69