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I would like to share my opinion on this matter; perhaps it will address many of the questions.
1. The main advantage of SoD is that it has been the default version for players coming from offline play for many years. This doesn't mean that SoD is better than TE, but it is its clear and main advantage. Almost all new players are SoD players, and this is no secret.
2. The main incentive for most players to try TE is to play against players like Stinger and Co. (although Paladin can play SoD without any problems, and others too). At this point, they are not focused on analyzing why TE is better. But, as someone rightly pointed out, tournaments on Battle.net are played on TE, which significantly distinguishes this game from the familiar SoD. Players simply understand that they will at least need to relearn, adapt to the possibilities of new options, etc., and before that, trying to compete with the TOP players on their "territory" is simply pointless. This creates a vicious circle.
3. Here is a personal example. I have always played SoD. At first, it was very difficult, then just difficult, and over time, mainly thanks to games with Paladin, I understood what and why, and some ambitions appeared. I also played a few games in TE. No one doubts that the interface is a clear plus. I understand most of the innovations, and moreover, I approve of them. In general, I agree that TE is more balanced and that the tasks set were implemented. BUT! This is the most important "but," and no matter what anyone says or what arguments they give. As a SoD player, I simply don't believe them. So, this "BUT" really lies in the fact that I don't want to delve into or, more precisely, spend time mastering all the new features of TE (I emphasize again, even the positive ones). The first reason is simply laziness or conservatism. The second is the realization that, by playing TE, you will first take a serious step back in your gaming skills until you understand the simple things at the level of the majority. The elementary balance adjustment of all second-level creatures and the presence of three stacks for starting heroes already create different expectations for certain castles. Adding to this the elementary balance possibilities of accelerated construction (for example, upgrading wolves for Barbarians) makes them clear favorites in TE (which, when I first encountered TE, I didn't realize), and so on. You can continue for a long time, but the essence is the same: some castles have been weakened, and some have been strengthened for balance, but this is no longer SoD in terms of strategy.
These are the main reasons why it is difficult for SoD players to switch to TE.
4. Online gaming time. Here, in my opinion, I judge by myself. I have been playing online since 2007 - not that long. Considering that all TE players play online much more, I cannot claim that by, say, 2010+, I will not get tired of the imbalance of SoD and I will not start playing TE. However, there is also a difference here. As I understand it, at one time, TE was mastered by a certain group of people together, in approximately equal conditions, and no one felt a gap in skill, which was perceived as intended.
5. The wrong approach to assimilating TE players with SoD players. A correct step was taken by Vic in the form of TE-Lite. Realizing that there are no changes - only the interface (although at first, even the notifications about resources taken instead of a window, which no longer required an extra click, were more annoying than simplifying the game - for example, I was looking to see what I had taken - 500 gold or 5 gems, etc.), many "decided" to try it, and I think everyone, including me, agreed that transferring troops with one button and splitting units is progress. But it didn't go any further. To absorb all the depth of thought and innovations of TE-Full, which were developed by the TE players themselves, is very difficult for a SoD player; he simply chokes on the flow of information, not as such, but on the attempt to immediately extract from it the benefits that have already been extracted by experienced TE players. It would have been necessary to hold tournaments on TE-Lite, gradually including one or another option, and I am sure that the desired result would have been achieved.
I remember that about a year ago, Vladimir suggested that I play a fun game in TE, and I agreed. To be honest, I liked it, especially the chess clock and fast travel. Yes, you can argue about many things (for example, the balance of magic, moving transport spells to fire and water so as not to create an imbalance with earth and air - and what? - in TE, everyone now uses water and fire :D), but if you say - guys, TE-Full is better than SoD - let's play TE - it won't work. And no one wants to play a fun game with someone in TE-Full or to look like a noob in serious tournaments.
Only a few have independently mastered and perfected all the advantages of TE. In my opinion, this is the objective result. Perhaps, as Armageddon said, there is not much point in promoting TE, as everyone has a real life and their own problems. And SoD does not need to be promoted - it is the default...
P.S. - for a tournament where there will be TE players and SoD players, TE-Lite is an undeniable compromise.