I have been an intensive (but not Power) user of Windows, Office and OneDrive for years both at work and home for as long as they've been around. For personal use, I went across to Mac about a year ago (had iPhones and Apple TV for several years, now have MBP, iPad, Studio display, Watch and AirPods Pro). My wife still uses a Windows laptop and is unlikely to change any time soon - she likes what she's familiar with.
So, as a relative newcomer to a Mac (and therefore I'm still learning) here are my thoughts:
Firstly, 365 on Mac: In general Office and OneDrive work just fine - I can't say I have noticed any significant differences. I would also say that they (particularly word) seem to be a lot more stable these days than they used to be.
Secondly, "Office lag": I wasn't aware of it but went and tried it on my wife's machine and agree, first opening is quicker on hers (and I have a faster processor). That said, I realise now that I never knowingly close word and excel and don't see why that would be a need these days. Then again, I have a lot of RAM. I think Macs use regular disk space these days if they run short on RAM. On reflection, I just see no benefit to changing my practice. YMMV but I'd invite you to consider whether your practice today is dealing with a historical issue.
Thirdly, I think there's more to the decision to move across to a Mac than those and I would counsel considering the broader picture:
There are some initial downsides for a Windows user:
- The UI has quite a lot of differences - they just take some time to get used to. Some of the functionality is quite well hidden - Google is your friend!
- No delete key on MBP. There is a workaround "fn backspace"; it's OK but it's not the same.
- Mac Finder is nowhere near as good for me as Windows explorer or I need to learn how to use it better.
- Splitting screens (windows key + arrows). There is an equivalent function but it's steam age by comparison.
- I use Office (including Outlook over the Mac equivalents - as others have said they are a must for my needs.
- Some apps don't have Mac versions. I have an organiser app (MLO) that falls into this category. Fortunately you can buy something called Crossover that allows you to run Windows programs and this works pretty well. It's not seamless but, for me, good enough on MLO.
- Some key apps (e.g. WhatsApp) not available on iPad.
Then there are some things I really like:
- Performance: yes you pay but Apple silicon (at least as of a few months ago) seems to comprehensively outperform Intel chips. You wouldn't bet against Intel catching up though. The biggest benefit for me is battery life - my MBP last all day while I had never had a Dell that lasted more than a (very) few hours.
- The charges are light and extremely fast.
- Comprehensive integration between devices.
- Calendars, photos, Notes, probably others, all sync seamlessly between devices. My wife and I share selected calendars via her iPhone, works pretty well although I have discovered that some minor data (e.g travel times doesn't get received at the other end).
- I have set up my Studio display with my MBP open on a tray next to it and the extended displays work quite well. I today discovered that I can extend the display wirelessly to my iPad. I believe that you can use your iPhone as a camera for your laptop but haven't tried that yet.
- My Watch automatically unlocks my MBP.
- Great display.
- The hardware by all accounts has amuch greater longevity I know and read about people who have devices still running happily after 10 years. My Dells at least usually started showing their age after 2-3 years.
- I am an amateur photographer and Apple silicon seems to be very well suited to post processing apps.
- My MBP hooks up wirelessly from my armchair to my Apple TV to use my Samsung TV as a big monitor. All I do is press the MBP share button and both the Apple TV and TV itself both get turned on.
- I use a Logitech keyboard and mouse at my workstation - they work seamlessly.
- I had all sorts of fun and games with Windows updates over the years, thus far at least, not a single issue with my Mac.
Would I go back if I could get my money back? No.
Best of luck, whichever way you go!