Read the first sentence of the OP.
Exactly. If at max budget buying a 3090 and pairing it with a 3570k which you wont be able to upgrade in the near future is going to give you a worse gaming setup and performance than a 3070/3080 and a mid range modern cpu.
Exactly the same principle as investing in a 3090 for this platform. You pick a 'balance' for the overall system and the needs for X budget, for a gaming rig 16/32GB
What people, backup for this? Lets go along with this though. So you buy a 1080Ti in 2017 at >$700 but you pair it with a q9650 (9 year old cpu in 2017) for gaming which is inadequate for some games. The gpu is significantly under utilised and gives no useful benefit over maybe a 1060 6GB/1050Ti and then run this bad setup for 3 years, then at the end of 2020 you look to upgrade the cpu? The money put into that GPU horsepower you never used could have been put towards a better cpu platform and given a much better gaming experience in the last 3 years. That under utilised 1080Ti in late 2020 is missing features that newer cards have, no RT, no HDMI 2.1, and so on. You now desperately need a cpu upgrade but you blew the budget on a gpu you never got close to fully utilising and if you want to make use of new game and hardware features you may start wanting to upgrade the gpu again. While you definitely do not need to completely upgrade your whole system every time a new gpu comes you have to look at this as an extreme case of pairing the highest end gpu today (3090) that costs the same as a whole mid range system with a cpu that is 7 generations old and barely entry level by todays standards, I see no benefit and looks to be a waste of money in the long term if now unable to upgrade the cpu in the near future.
It is offensive to say "No, it is absolutely retarded to do this. " in reply to a post and implies you are calling the poster retarded. It was slightly offensive to say "Worrying if the setup is balanced is actually really stupid " in reply was slightly less offensive but again implies you are calling the poster stupid. I deliberately used your own wording back to you the first time in hope you would get the point.
Apologies to the OP . I will try not to respond to these comments again and will try and help with any further questions you have.
I welcome discourse, but don't get an attitude or rude with me.
Given the premium on the newest cards won't go away for a while, the OP saved right there. And if that's 6 months, and if OP is stretching the i5 for 1yr, that's only really 6 months where there may be some sort of appreciable 'loss'. OP wasn't after an optimal performing setup, just a stretch of the existing one. Otherwise the answer to every single upgrade question would be 'buy a new setup' (which is too often the answer stated on here even though it's wrong).
There's posts on here--person got bashed for it too. Do the search. There were at least 2 threads like this in the last year. Person got the 1080Ti for cheap/free in both cases.
Offensive is on the receiver. Anyone can find anything offensive. Your accusation was that of a personal attack. A personal attack would have been, "You are absolutely retarded to do this." If you strip away all the other clauses in this sentence, it reads 'You are retarded', which is a personal attack. Now, let's examine what I posted, "No, it is absolutely retarded to do this." Strip away the extra clauses and you have 'it is retarded'. It is referring to the concept, not you. Again in all the clauses you are referencing, I am directly talking about the topic at hand--"Worrying is stupid." At no point does this indicate an inference to the person making such a decision, nor was that my intention. Again, I find the idea that a system must be balanced to be stupid, not the person who thinks this.
OP is probably long gone with their answer as is common in these threads, so I wouldn't worry about offending them. They also got to see the pros and cons for both a balanced and unbalanced setup and can make up their own mind.