I dont think he meant it as a negative criticism, I appreciate his feedback and I also sort of do understand why at first sight it looks like MT should be easy to make responsive when you see the block structure.
The problem is that it is hard to explain unless he would install it himself to see how it works. Technically, using blocks is exactly how you make a fully responsive site. On wider screens you put the blocks next to each other and as the screen gets narrower, you start placing them on top of each other - this is how for example bootstrap works.
Thats all nice until you consider that in this case, you as a webmaster choose the number of columns, then there are also menu and multiple blocks, subblocks... header block, footer block, all this gives you lot of possibilities of how you can build your site, but if I was to make it fully responsive, I would again have to be the one who "takes control" and decides, ok, well this block will go here, this one here.... and thats exactly what I dont want to do. My goal was always to create a very customizable template, which however can be fully customized without knowing the code. It is not just the column number, it is also the column width the user can set and last but not least - it is also the blocks themselves. Each user has absolutely unique combination of blocks and they choose the column number and width which looks best for those particular blocks. It is not just rearranging them on the homepage, it is actually choosing them.
And I have also emphasized, that the code is obviously 100% open source which means there is absolutely nothing preventing you to simply take it and do whatever you want with it. And if you are familiar with PHP you could surely make YOUR webpage fully responsive even using Meteotemplate, its just that this is something I cannot build-in to it simply because you can do it to your site but not a generalized script that would work for all.