The extra attack feat could cause problems IMO and will gimp non-casters even more than they already are gimped in 5E. If I was powergaming, a Bladesinger 8, Swords Bard 7, Battle Smith Artificer 5 would just be way OP. That character would have martial weapons, a fighting style, expertise, Jack of AT, a pet, the best AC in the game and the best version of extra attack in the game along with 6 ASIs and 9th level spell slots.
The thing is even if you make that character take feats and not ASIs, they can take ASIs with their regular feats. Multiclassing already outruns single class characters even with the lost ASIs.
wow, extra feat over single class bladesinger 20?
and 9th level spell slots do not mean much when your highest level spell is 4th.
unless you mean to abuse CME, no much use of it.
and pet is complete trash at 20th level, best armor does not stack with bladesinging, still limited to light armor.
can you make a versatile character this way. 100% yes. and it would be fun to play.
Is it more powerful than 20th level bladesinger? No.
and replacing extra attack with a feat is a decent trade.
you need to ask a question?
would you spend a feat to get Extra attack.
yes!
even a "full" feat from 2014, without +1 ASI?
yes, 100%
it almost doubles your DPS, no feature does that.
even would spend a full feat at 12th level for fighters extra-extra attack, even if then it only increases your DPS by 50%.
maybe a choice between epic boon and 20th level fighter extra-extra-extra attack is a choice to be made?
does +33% DPS performs better than another epic boon?
extra attack is the most powerful feature in the game, outside high level spells and maybe paladins aura.