It seems that you are saying that small cell will eliminate or reduce the issue of varroa but that people dismiss it in their striving for varroa resistance. I have started trying to introduce foundationless frames into my hive, but it seems the bees still build pretty big cells in it.
If you put a foundationless frame in a hive with a bunch of 5.4mm drawn foundation, the bees are going to make pretty large cells to start with. The bees themselves are large, since they came out of large cell, so they are going to make pretty big cells... maybe 5.1 mm. And since the foundation has not afforded them an easy opportunity to make drone cells, the first thing they do when they have a chance to make their own comb is to make lots of drone cells.
To get the bees to make natural comb, the bees need to be hatched from smaller than 5.4 mm cells or given lots of encouragement. One way to encourage them is to put them on Mann Lake PF plastic comb with 4.95 mm cells. This guides them to draw the smallest cells they are capable of. Then you can start adding foundationless between the pf frames.
But as long as you leave standard foundation in the hive, you will continue to make big bees. That's the hardest thing about getting to natural cell or small cell. You have to get the old comb out of the hive. That hurts because drawn comb is such a valuable commodity, but it's better to get it out as soon as possible. You can move it to the sides and up over time, or just trash it. I would say trash it if you are able.