I think klassy's post summarises most of my thoughts, I just have a few to add from a soldier/maincallers perspective.
old patch is fast medics
new patch is slow medics
Firstly looking at the change from a soldier main perspective. I think the gunboats buff is insanely powerful for soldier. Our team has scrimmed with the plugin for a month, soldier feels unbelievably easy/easier to play. Removing the option for scouts to run inside you so that you take 80-100 self dmg means you should never lose a 1v1 in a small area. And even if you are losing a 1v1 you can just leave as the scout cant just run into you as you're leaving anymore. I am really against the opinion that soldier is/used to be a "weak" class. You have so much impact on the game as soldier (in both the old and new patch). I believe people complained way too much about soldier being useless when they were actually just misplaying situations, or maybe its because people judge their performance based on their k/d. Now adding the med speed change just makes this patch an ultra buff to soldier. I am not against ingame changes and think its very valuable to try new rulesets/plugins. However as klassy already said this change basically just decreases the pace of the game whilst also buffing soldier.
Now looking from a maincallers perspective. If you're the maincaller for your team, you will have had to completely change your style of calling over the past month (again I am not against plugin changes forcing maincallers to adapt). On the old patch in a even situation many very aggressive plays were reasonably safe (assuming both team have uber). However on the new patch it feels like you have to call in a much more controlled/safe style where you cannot take the risks you used to be able to. This limits your options a lot and therefore makes the pace of the game slower. When you have ad you cannot extend it anywhere near as much as you used to be able to, which makes you settle for map control which again slows the game down. One change that is very nice as a maincaller is that the mid fights are more important than they used to be. In my opinion tf2 has always been a game about midfights and this patch makes it even more prominent, I like this change as it rewards your team for coordinated team fights and instinctive plays.
My biggest issue with EU playing on the new patch is that we're playing on a different patch to everyone else who plays the game. I think the smaller plugin changes such as the no ramp bug plugin and others are fine as they're just quality of life improvements, but the med speed completely changes how EU and the rest of the world play the game. Of course my opinion is biased as I am someone who wants to play/compete at intercontinental lans and maybe this issue isnt as relevant to the avg comp player.
I believe to best solution for EU/ETF2L is a patch where the quality of life plugins are added but the med speed is reverted to the old patch. In my eyes soldier has been buffed twice in the new patch. Once because of the gunboats plugin and once because of the med speed change. Going back to the fast medic patch is essentially a trade off between removing a 2nd buff to soldier but making the game faster and more aggressive. I think this proposed patch is what ETF2L should change to in the future (s38). This patch would solve the issue of intercontinental lans as these quality of life changes wont change the macro teamplay of the game. When a lan happens no ones going to complain whether you always slide on a ramp or not. I still think s37 should be played on the current ETF2L patch as it would be too late/confusing to change the ruleset again.
I do still enjoy the game on the new patch but I think the overall teamplay is more skilled and fast paced on the old patch.