Think we mix up issues and then get into controversy.
1. Demand and supply are intrinsic to the working of the market. Without buyers and sellers interacting , their activity being reflected in transactions ie. volume, there would be no market. Hence volume is activity or effort if you like to put it that way and the resulting move or lack of it, is the result of that activity. Wyckoff studied this aspect and understood it well enough to read the market to be able to anticipate and trade.
2. Now one can choose to study these price/vol dynamics and incorporate them into their trading strategies/tactics. For that trader Volume is important. We are not talking about DOM, time/sales, bid/ask etc here.
3. Others and there are many successful traders doing just that, trade without looking at the volume bars on their charts and employ other technical analysis to guide and provide them with aa framework and structure to trade ie. RSI, CCI divergence, fib numbers, gann, elliot , candlestick patterns, moving averages etc.
Infact if you look at Al Brooks latest book, he trades entirely from just one single 5min chart with one moving average and trendlines/channels. I have communicated with him, he has gone through every indicator out there, including volume studies and probably understands the patterns that he outlines in his book well against that background, so he does not need to have the volume bars on the chart. However he does mention volume climax etc and many of the charts in the book do have vol. bars.
So it appears that that if you study price/vol long enough and observe the patterns forming just like looking at RSI divergence and price action long enough, you eventually reach a point where you may not require these on the charts.
Anyway the point of all this is Volume is the engine which drives the market.
However whether it is important to trading is a personal choice. Hence as you say there is nothing right or wrong. So really there should be no clashes between those who use it and those who do not,

))