I'm no expert on Vacuums, but I have read a bunch on this forum and on the subreddit, as well as youtube. Due to recommendations I have recently purchased a Sebo D4 to compliment my Oreck machines (XL21 and IronMan). I could have had my late grandmother's 1987ish Kirby for free.
I think what we've determined is that there's a lot of good vacuums, but what you're doing with them will matter a lot. The Kirby I found impractical - the size and weight and difficulty for people in my family to service it just make it mostly non-working a lot of the time (it's pretty complicated to change a belt or unclog compared to the XL21 anyway - it also weighs 3x or more as much).
The Oreck XL21 was great when we had a LOT of open carpet, but it's not practical for us once we replaced the living room flooring with laminate and throw rugs. (The Orbiter now... it's very practical, but you have to vacuum or sweep first).
The Sebo seems to have the best of both worlds - it's not as light as the Oreck, but it's not as heavy as the Kirby. The ET-1 Powerhead is as even more maneuverable than the XL21, and can get in places the Upright sort of struggled with (we have too much stuff making open areas very non "straight" and lots of chairs to dodge). It has the brushroll off option the XL21 doesn't so we can switch to area rugs or the couch without switching vacuums like we had to with the Oreck XL21 to Iron Man).
Now, maybe we never had the "right" carpets (my grandmother got the Kirby for a a very low pile, and an almost felt over concrete carpet) - but the Kirby never cleaned in any amazing way. We also never hauled it over to the medium carpets for any testing, so IDK if it would have blown away our Orecks there either. But it never really impressed me for anything except being a tank and the little penny catcher thingy. Maybe we just never really understood how to use it either. But no other vacuum I've seen required any special knowledge to use reasonably well. So I really don't get the Kirby love - at least for us it is a great conversation piece, but isn't ever actually used by anyone.
I wonder if the Vacuum Tech on Reddit is actually basing on price (the Sebo D4 was like $200 or more less than the Kirby, and the Kirby sales is very sketchy for new per the net) and what normal people *might* actually be able to do.
I will say, I agree with him that I don't like bagless (too messy to empty, have to go outside and vacuum the bagless with a different vacuum almost lol), and I wouldn't recommend a Wal-Mart or Best Buy vacuum. The XL21 is still running after 11 years, we would kill the "cheap" ($200) vacuums every 6 months to 2 years. After 3 of those, we decided to risk the $750 on the Oreck, and not only have we not had vacuums breaking seemingly all the time, we also haven't had to buy another - the Sebo was for convenience and getting out of sweeping... Even considering that the needs changed, we paid $750 for 11 years vs probably closer to $1200 and 6 hassles of replacing a useless "cheap" vacuum.