Should I Separate One Of My Fish To Help It Get More Food ?

I have 6 angelfish of all different colour variations in a 125 litre tank. I've had them for about 4 months and I plan to move them to a 450 litre tank soon. They've all been growing well apart from one. He/she seems to be the odd one out and even swims a bit weirdly. But I still love him/her the same and have named him/her Pirate due to his black eye patch. The problem is he/she tends to get out competed for food and is about half the others' size. I have another tank (65 litres) which is bare bottom at the moment but I suppose I could buy some plants and gravel for it. I was wondering whether it would be best to move him/her into it. However I do plan on breeding them eventually and I want them to form pairs. If I do this should I move him/her into it along with another fish ? When I move them into the 450 litre tank I don't want him/her to be bullied. Or should I just leave him/her to avoid stress of moving? Any answers would truly be appreciated!

Thanks for your reply @Matt ! Yh my friend said that too. I usually try to confuse them and reset the hierarchy by changing up their territories every time I do a water change and he/she never seems to rise to the top But yh spot feeding sounds like an easier option. He/she usually waits below the others to catch what food they miss. So I'll try and distract them while feeding him/her. Thanks so much that was helpful !