So as a 1.8 user i really love to not go about changing versions, i think that GTM should revert back to the old way of texturing things, using individual items for each texture, this therefore means that 1.8 users who cannot support the pack are able to play without the massive Pink and Black blocks in their hands, and also I personally do not like using the pack, I'm very much used to seeing tools as weapons, also as for the diamond swords, they are not stackable in vanilla MC, therefore if they become unstacked its hard to restock them as they are not actually stackable, this allows grenade users to be able to stack up to 65 again.
I'll give you my opinion, The game is soon getting 1.13, and you're still in 1.8. It's Time to change! Change is always better, and if it's the new PVP system you're getting away from, This new one isn't all about jitterclicking, It now takes strategy, wich is better. The new versions also have loads of cool stuff!! I recommend using 1.12.
We heavily discourage usage of any version below the latest supported version, ESPECIALLY 1.8. We realize that it is not ideal for you to have to switch between versions to go on other servers, but maybe the other servers should be the ones to make the change. 1.8 PvP is possible on all Minecraft versions, either through version protocol support or through pvp plugins, both of which are publicly available). I don't know why servers would not allow 1.12 players to join. TL;DR: Please use 1.12 when playing on GTM, and ask other servers to support the latest version.