you may very well be slowing the piece too much to learn it, a symptom of likely learning works too far above your ability level or familiarity w idiom, style, etc.
do you have the same criticism with works well below your current level? , if not, then isolate at what difficulty cohesiveness and overall pulse suffer, then back it off a little.
yes is it ok to play a little less brisk for the sake of control, but the tempo is part of the music, and a piece will lose its character when taken too slow, its a score marking and should be followed, if you are not able to, the piece may be too much for you right now at least.
for pulse and overall flow, you need to learn to listen to a piece and 'feel' it in overall pulse, ie a 4/4 work, will tend to many times have a feel of a 2 big beats per measure, also, beats don't have equal emhasis, same 4/4 beats 1 and 3 usually stronger and playing them with a 'down' motion works well a lot of the time, beats 2 and 4 generally weaker, an up motion works better, similar can be said for 6/8 , where really should be felt in '2', 3/4 usually one large beat 2 leading up beats,
tempo, can be addressed with systematic pushing beyond the performance goal, so once the exam or performance comes you have it in your hands beyond the called for or your own goal to play. when you perform, it is seldom a smart idea to be at your max, too many things can go wrong, so something you aim to play at 110-130, be comfortable w tempi at 140+ so you're in complete musical and technical control, this allows you to plan and listen actively and make spur of the moment calls and adjustments mid performance since your mind isn't so occupied w notes at a breakneck for you speed, you can focus on other aspects of the performance which are, and should be many.
so weeks/months out you have the piece at 90, you work on overal large beat feel and set a goal for the week to push it to 98, the following week, 110, then maybe two weeks later 120, then a week later 135, then 140, then hold a few weeks, then back it off to 120... that's what i do at least.
a lot of hist stuff gets covered in training at the university/conservatory formal study and advanced private studio (with appropriate teacher) instruction, i recall ranjit asked about stuff liked that elsewhere recently