Should I get endwalker if...

[Akiudo]

For button spamming, there are third party solutions like "turbo" key and even gamepads with "turbo" mode for buttons (does the fast mashing for you).
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if you are on pc and use m/kb there are also autoclickers, simple programs that simulate you hitting your mouse button 100 times a second or whatever you want, so that problem while existing can be easily worked around.

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now about the raid issue, that depends on you i would say. the 24 man raids have a lot bigger areas, quit possible you could work better in the normal mode raids simply because the areas are smaller, but even if not i would say is that really important ? obviously if you totally want to do some form of raiding at least than sure, but there are many other things to do in the game so that by itself i wouldn't say is a reason not to buy endwalker.

just one small thing, you mentioned having to watch all these things while you have to keep up with your dps. on that i will say that for normal modes no one really will care if you do subpar dps so don't sweat it, people will care a lot more about someone killing the group by failling mechanics, having someone doing subpar dps (if that is the result of you focusing 90% of your energy on mechanics) is basically expected when people use df.

IF you wanted to do savage though i will give you a completly different advise, which is to stop thinking about your dps all the time. in general if you actively want to do savage you should get your rotation so hard into your muscle memory that you "just do it" instead of actively watching out for it which would somewhat solve your problem i guess ? kinda depends if you can reach that point, in the end though its mostly doing enough repetitions that it becomes second nature and nothing else.