RANT
I can play with mostly all weapon classes; Main the ink brush variants, Custom Jet, Carbon, splat roller. The only class im not too familiar with would be the blasters but Ive been getting in the swing of things with the custom blaster recently. Now contrary to popular belief, every weapon is viable even the ink brush(both versions.) when it comes to the ink brush it really depends on whos using it. Its turf covering ability and mobility are also very good. It lacks range and power but if you have a good trigger finger and are good with movement you can go toe to toe with a gunner. people write it off because of its poor range and its huge difficulty curve but honestly you should play what you want. If everyone just played 'high tier weapons' then this game wouldnt be fun nor would it evolve.
Though I dont think it matters much, I figure id say this for clarification; I am an S+ ink brusher and ive definitely been in your shoes dude/dudette(?) having people reject me from a squad because I choose to use the ink brush. It sucks and its kinda stupid but thats how things are and to be honest, having people underestimate something so much makes me want to use it more, get really nice and reck face in a tourney to the point that people will need to rethink their opinion on said weapon. I used to use the vanilla ink brush religiously because it had the throwable sprinkler but ive recently picked up the nouveau. Ive come to realize that the nouveau is pretty beastly when you stack damage ups on it to increase its effective range so even if they try to knock you out of range when you bubble, you can still dish out heavy hits from far away. Special savers work as well.
I also try to not heavily engage unless I have bubbler online which isnt difficult for the ink brush since it specializes in gaining special quickly. Moral of the story: dont let anyone sway you from using a weapon. To be honest I have a competetive gaming background from Halo to Smash to Guilty gears to yugioh etc but I kinda wish this game wasnt so competitive so that people can start using different weapons in ranked and tourneys, really starting to see the same weapons.
/RANT
Now as for your issue; it seems like it is not so much the ink brush as it is the player... no offense. It is important to learn other weapons to not only understand their strengths and weaknesses but by learning other weapons, you tend to pick up certain playstyles and implement them into your main weapons playstyle which can be very useful. For example: Playing chargers taught me patience and accuracy while playing guns taught me how to play in a firefight and playing rollers, especially the ink brush, taught me movement and how to be crafty by using different walls and such instead of just hiding in ink on the ground.
It sounds like you lack some basic skills and more importantly a certain shooting game mind set you should have.
Try to follow these 3 rules when on the field:
1. Never stay still.
Even when you have the objective and the whole enemy team is dead try to cover ground or slowly push into the enemy territory. Im not saying to go spawn kill but just make sure you arent in one place just squidding in ink until the enemy team respawns. Obvious exception is if you are about to strike a foe down in front of you. and you dont want them to know where you are.
2. Spread out.
I personally try to go everywhere my team isnt. unless they need my help or if I have bubble since I play Nouveau. Going a different route allows you to set up a possible flank that can potentially win your team the game.
2.5 Use the walls.
The walls. Use them.
3. ALWAYS be aware of your surroundings.
Probably the most important and most overlooked rule. You should always be swinging your camera around to make sure no squid is sneaking up on you, if you know someone is around a corner try to pan your camera around the corner to set up a strike instead of a blind, all in no fear attack. Make sure there is no enemy ink around you or your squad mates lest there be an enemy squid hiding in it.
Try to apply these rules, get used to using other weapons, and also keep practicing. We need more good ink brushes out here.